Add a no-op platform view layer. (flutter/engine#6505)

This will be used for embedding UIViews on iOS.

Landing a no-op layer as a first incremental step to keep PRs small.

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -556,8 +556,10 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 ====================================================================================================
 LIBRARY: engine
-ORIGIN: ../../../flutter/flutter_kernel_transformers/lib/track_widget_constructor_locations.dart + ../../../LICENSE
+ORIGIN: ../../../flutter/flow/layers/platform_view_layer.cc + ../../../LICENSE
 TYPE: LicenseType.bsd
+FILE: ../../../flutter/flow/layers/platform_view_layer.cc
+FILE: ../../../flutter/flow/layers/platform_view_layer.h
 FILE: ../../../flutter/flutter_kernel_transformers/lib/track_widget_constructor_locations.dart
 FILE: ../../../flutter/fml/paths_unittests.cc
 FILE: ../../../flutter/lib/ui/isolate_name_server.dart

engine/src/flutter/flow/BUILD.gn

@@ -34,6 +34,8 @@ source_set("flow") {
     "layers/physical_shape_layer.h",
     "layers/picture_layer.cc",
     "layers/picture_layer.h",
+    "layers/platform_view_layer.cc",
+    "layers/platform_view_layer.h",
     "layers/shader_mask_layer.cc",
     "layers/shader_mask_layer.h",
     "layers/texture_layer.cc",

engine/src/flutter/flow/layers/platform_view_layer.cc

@@ -0,0 +1,21 @@
+// Copyright 2018 The Chromium 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/flow/layers/platform_view_layer.h"
+
+namespace flow {
+
+PlatformViewLayer::PlatformViewLayer() = default;
+
+PlatformViewLayer::~PlatformViewLayer() = default;
+
+void PlatformViewLayer::Preroll(PrerollContext* context,
+                                const SkMatrix& matrix) {
+  set_paint_bounds(SkRect::MakeXYWH(offset_.x(), offset_.y(), size_.width(),
+                                    size_.height()));
+}
+
+void PlatformViewLayer::Paint(PaintContext& context) const {}
+
+}  // namespace flow

engine/src/flutter/flow/layers/platform_view_layer.h

@@ -0,0 +1,39 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_FLOW_LAYERS_PLATFORM_VIEW_LAYER_H_
+#define FLUTTER_FLOW_LAYERS_PLATFORM_VIEW_LAYER_H_
+
+#include "flutter/flow/layers/layer.h"
+#include "third_party/skia/include/core/SkSurface.h"
+#include "third_party/skia/include/gpu/GrBackendSurface.h"
+#include "third_party/skia/include/gpu/GrContext.h"
+#include "third_party/skia/include/gpu/GrTexture.h"
+#include "third_party/skia/include/gpu/GrTypes.h"
+
+namespace flow {
+
+class PlatformViewLayer : public Layer {
+ public:
+  PlatformViewLayer();
+  ~PlatformViewLayer() override;
+
+  void set_offset(const SkPoint& offset) { offset_ = offset; }
+  void set_size(const SkSize& size) { size_ = size; }
+  void set_view_id(int64_t view_id) { view_id_ = view_id; }
+
+  void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
+  void Paint(PaintContext& context) const override;
+
+ private:
+  SkPoint offset_;
+  SkSize size_;
+  int64_t view_id_;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(PlatformViewLayer);
+};
+
+}  // namespace flow
+
+#endif  // FLUTTER_FLOW_LAYERS_PLATFORM_VIEW_LAYER_H_

engine/src/flutter/lib/ui/compositing.dart

@@ -268,6 +268,15 @@ class SceneBuilder extends NativeFieldWrapperClass2 {
   }
   void _addTexture(double dx, double dy, double width, double height, int textureId, bool freeze) native 'SceneBuilder_addTexture';
 
+  /// Adds a platform view (e.g an iOS UIView) to the scene.
+  ///
+  /// This is work in progress and is not currently supported on any platform.
+  void addPlatformView(int viewId, { Offset offset: Offset.zero, double width: 0.0, double height: 0.0}) {
+    assert(offset != null, 'Offset argument was null');
+    _addPlatformView(offset.dx, offset.dy, width, height, viewId);
+  }
+  void _addPlatformView(double dx, double dy, double width, double height, int viewId) native 'SceneBuilder_addPlatformView';
+
   /// (Fuchsia-only) Adds a scene rendered by another application to the scene
   /// for this application.
   void addChildScene({

engine/src/flutter/lib/ui/compositing/scene_builder.cc

@@ -19,6 +19,7 @@
 #include "flutter/flow/layers/performance_overlay_layer.h"
 #include "flutter/flow/layers/physical_shape_layer.h"
 #include "flutter/flow/layers/picture_layer.h"
+#include "flutter/flow/layers/platform_view_layer.h"
 #include "flutter/flow/layers/shader_mask_layer.h"
 #include "flutter/flow/layers/texture_layer.h"
 #include "flutter/flow/layers/transform_layer.h"
@@ -53,6 +54,7 @@ IMPLEMENT_WRAPPERTYPEINFO(ui, SceneBuilder);
   V(SceneBuilder, pushShaderMask)                   \
   V(SceneBuilder, pushPhysicalShape)                \
   V(SceneBuilder, pop)                              \
+  V(SceneBuilder, addPlatformView)                  \
   V(SceneBuilder, addRetained)                      \
   V(SceneBuilder, addPicture)                       \
   V(SceneBuilder, addTexture)                       \
@@ -217,6 +219,21 @@ void SceneBuilder::addTexture(double dx,
   current_layer_->Add(std::move(layer));
 }
 
+void SceneBuilder::addPlatformView(double dx,
+                                   double dy,
+                                   double width,
+                                   double height,
+                                   int64_t viewId) {
+  if (!current_layer_) {
+    return;
+  }
+  auto layer = std::make_unique<flow::PlatformViewLayer>();
+  layer->set_offset(SkPoint::Make(dx, dy));
+  layer->set_size(SkSize::Make(width, height));
+  layer->set_view_id(viewId);
+  current_layer_->Add(std::move(layer));
+}
+
 void SceneBuilder::addChildScene(double dx,
                                  double dy,
                                  double width,

engine/src/flutter/lib/ui/compositing/scene_builder.h

@@ -76,6 +76,12 @@ class SceneBuilder : public RefCountedDartWrappable<SceneBuilder> {
                   int64_t textureId,
                   bool freeze);
 
+  void addPlatformView(double dx,
+                       double dy,
+                       double width,
+                       double height,
+                       int64_t viewId);
+
   void addChildScene(double dx,
                      double dy,
                      double width,