Embedder: Refactor EmbedderTestContext creation (flutter/engine#56563)

Extracts creation of graphics backend specfic EmbedderTestContext creation to their own translation units. In particular, this allows for less conditional header includes, and more specifically, for code relating to the Metal backend to include headers that include Objective-C types -- today we cast these all to void* to avoid declaring them in headers, which requires special handling for ARC.

An alternative approach would have been to extract backend-specific subclasses, but there are test suites such as `EmbedderTestMultiBackend` that are executed against multiple backends, which make that approach impractical.

No test changes since this patch makes no semantic changes.

Issue: https://github.com/flutter/flutter/issues/137801

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

engine/src/flutter/shell/platform/embedder/BUILD.gn

@@ -317,6 +317,7 @@ if (enable_unittests) {
         "tests/embedder_test_compositor_gl.h",
         "tests/embedder_test_context_gl.cc",
         "tests/embedder_test_context_gl.h",
+        "tests/embedder_test_gl.cc",
       ]
 
       public_deps += [
@@ -331,6 +332,7 @@ if (enable_unittests) {
         "tests/embedder_test_compositor_metal.h",
         "tests/embedder_test_context_metal.cc",
         "tests/embedder_test_context_metal.h",
+        "tests/embedder_test_metal.mm",
       ]
 
       public_deps += [ "//flutter/testing:metal" ]
@@ -342,6 +344,7 @@ if (enable_unittests) {
         "tests/embedder_test_compositor_vulkan.h",
         "tests/embedder_test_context_vulkan.cc",
         "tests/embedder_test_context_vulkan.h",
+        "tests/embedder_test_vulkan.cc",
       ]
 
       public_deps += [

engine/src/flutter/shell/platform/embedder/tests/embedder_test.cc

@@ -5,20 +5,7 @@
 #include "flutter/shell/platform/embedder/tests/embedder_test.h"
 #include "flutter/shell/platform/embedder/tests/embedder_test_context_software.h"
 
-#ifdef SHELL_ENABLE_GL
-#include "flutter/shell/platform/embedder/tests/embedder_test_context_gl.h"
-#endif
-
-#ifdef SHELL_ENABLE_METAL
-#include "flutter/shell/platform/embedder/tests/embedder_test_context_metal.h"
-#endif
-
-#ifdef SHELL_ENABLE_VULKAN
-#include "flutter/shell/platform/embedder/tests/embedder_test_context_vulkan.h"
-#endif
-
-namespace flutter {
-namespace testing {
+namespace flutter::testing {
 
 EmbedderTest::EmbedderTest() = default;
 
@@ -33,28 +20,17 @@ EmbedderTestContext& EmbedderTest::GetEmbedderContext(
   if (!embedder_contexts_[type]) {
     switch (type) {
       case EmbedderTestContextType::kSoftwareContext:
-        embedder_contexts_[type] =
-            std::make_unique<EmbedderTestContextSoftware>(
-                GetFixturesDirectory());
+        embedder_contexts_[type] = CreateSoftwareContext();
         break;
-#ifdef SHELL_ENABLE_VULKAN
-      case EmbedderTestContextType::kVulkanContext:
-        embedder_contexts_[type] =
-            std::make_unique<EmbedderTestContextVulkan>(GetFixturesDirectory());
-        break;
-#endif
-#ifdef SHELL_ENABLE_GL
       case EmbedderTestContextType::kOpenGLContext:
-        embedder_contexts_[type] =
-            std::make_unique<EmbedderTestContextGL>(GetFixturesDirectory());
+        embedder_contexts_[type] = CreateGLContext();
+        break;
+      case EmbedderTestContextType::kVulkanContext:
+        embedder_contexts_[type] = CreateVulkanContext();
         break;
-#endif
-#ifdef SHELL_ENABLE_METAL
       case EmbedderTestContextType::kMetalContext:
-        embedder_contexts_[type] =
-            std::make_unique<EmbedderTestContextMetal>(GetFixturesDirectory());
+        embedder_contexts_[type] = CreateMetalContext();
         break;
-#endif
       default:
         FML_DCHECK(false) << "Invalid context type specified.";
         break;
@@ -64,5 +40,35 @@ EmbedderTestContext& EmbedderTest::GetEmbedderContext(
   return *embedder_contexts_[type];
 }
 
-}  // namespace testing
-}  // namespace flutter
+std::unique_ptr<EmbedderTestContext> EmbedderTest::CreateSoftwareContext() {
+  return std::make_unique<EmbedderTestContextSoftware>(GetFixturesDirectory());
+}
+
+#ifndef SHELL_ENABLE_GL
+// Fallback implementation.
+// See: flutter/shell/platform/embedder/tests/embedder_test_gl.cc.
+std::unique_ptr<EmbedderTestContext> EmbedderTest::CreateGLContext() {
+  FML_LOG(FATAL) << "OpenGL is not supported in this build";
+  return nullptr;
+}
+#endif
+
+#ifndef SHELL_ENABLE_METAL
+// Fallback implementation.
+// See: flutter/shell/platform/embedder/tests/embedder_test_metal.mm.
+std::unique_ptr<EmbedderTestContext> EmbedderTest::CreateMetalContext() {
+  FML_LOG(FATAL) << "Metal is not supported in this build";
+  return nullptr;
+}
+#endif
+
+#ifndef SHELL_ENABLE_VULKAN
+// Fallback implementation.
+// See: flutter/shell/platform/embedder/tests/embedder_test_vulkan.cc.
+std::unique_ptr<EmbedderTestContext> EmbedderTest::CreateVulkanContext() {
+  FML_LOG(FATAL) << "Vulkan is not supported in this build";
+  return nullptr;
+}
+#endif
+
+}  // namespace flutter::testing

engine/src/flutter/shell/platform/embedder/tests/embedder_test.h

@@ -14,8 +14,7 @@
 #include "flutter/testing/thread_test.h"
 #include "gtest/gtest.h"
 
-namespace flutter {
-namespace testing {
+namespace flutter::testing {
 
 class EmbedderTest : public ThreadTest {
  public:
@@ -29,6 +28,11 @@ class EmbedderTest : public ThreadTest {
   std::map<EmbedderTestContextType, std::unique_ptr<EmbedderTestContext>>
       embedder_contexts_;
 
+  std::unique_ptr<EmbedderTestContext> CreateSoftwareContext();
+  std::unique_ptr<EmbedderTestContext> CreateGLContext();
+  std::unique_ptr<EmbedderTestContext> CreateMetalContext();
+  std::unique_ptr<EmbedderTestContext> CreateVulkanContext();
+
   FML_DISALLOW_COPY_AND_ASSIGN(EmbedderTest);
 };
 
@@ -36,7 +40,6 @@ class EmbedderTestMultiBackend
     : public EmbedderTest,
       public ::testing::WithParamInterface<EmbedderTestContextType> {};
 
-}  // namespace testing
-}  // namespace flutter
+}  // namespace flutter::testing
 
 #endif  // FLUTTER_SHELL_PLATFORM_EMBEDDER_TESTS_EMBEDDER_TEST_H_

engine/src/flutter/shell/platform/embedder/tests/embedder_test_gl.cc

@@ -0,0 +1,15 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/shell/platform/embedder/tests/embedder_test.h"
+
+#include "flutter/shell/platform/embedder/tests/embedder_test_context_gl.h"
+
+namespace flutter::testing {
+
+std::unique_ptr<EmbedderTestContext> EmbedderTest::CreateGLContext() {
+  return std::make_unique<EmbedderTestContextGL>(GetFixturesDirectory());
+}
+
+}  // namespace flutter::testing

engine/src/flutter/shell/platform/embedder/tests/embedder_test_metal.mm

@@ -0,0 +1,15 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/shell/platform/embedder/tests/embedder_test.h"
+
+#include "flutter/shell/platform/embedder/tests/embedder_test_context_metal.h"
+
+namespace flutter::testing {
+
+std::unique_ptr<EmbedderTestContext> EmbedderTest::CreateMetalContext() {
+  return std::make_unique<EmbedderTestContextMetal>(GetFixturesDirectory());
+}
+
+}  // namespace flutter::testing

engine/src/flutter/shell/platform/embedder/tests/embedder_test_vulkan.cc

@@ -0,0 +1,15 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/shell/platform/embedder/tests/embedder_test.h"
+
+#include "flutter/shell/platform/embedder/tests/embedder_test_context_vulkan.h"
+
+namespace flutter::testing {
+
+std::unique_ptr<EmbedderTestContext> EmbedderTest::CreateVulkanContext() {
+  return std::make_unique<EmbedderTestContextVulkan>(GetFixturesDirectory());
+}
+
+}  // namespace flutter::testing