[Impeller] test empty snapshot and allocation failure. (#164668)

Speculative fix for https://github.com/flutter/flutter/issues/164628

If our render target allocation failed, we need to bail out of toImage
so that we don't crash. Adds a test that simulates this by asking for a
0x0 texture.

engine/src/flutter/impeller/display_list/aiks_dl_unittests.cc

@@ -21,10 +21,12 @@
 #include "flutter/testing/testing.h"
 #include "fml/synchronization/count_down_latch.h"
 #include "imgui.h"
+#include "impeller/base/validation.h"
 #include "impeller/core/device_buffer.h"
 #include "impeller/core/device_buffer_descriptor.h"
 #include "impeller/core/formats.h"
 #include "impeller/core/texture_descriptor.h"
+#include "impeller/display_list/aiks_context.h"
 #include "impeller/display_list/dl_dispatcher.h"
 #include "impeller/display_list/dl_image_impeller.h"
 #include "impeller/geometry/scalar.h"
@@ -1104,5 +1106,18 @@ TEST_P(AiksTest, ToImageFromImage) {
   OpenPlaygroundHere(canvas.Build());
 }
 
+TEST_P(AiksTest, DisplayListToTextureAllocationFailure) {
+  ScopedValidationDisable disable_validations;
+  DisplayListBuilder builder;
+
+  AiksContext aiks_context(GetContext(), nullptr);
+  // Use intentionally invalid dimensions that would trigger an allocation
+  // failure.
+  auto texture =
+      DisplayListToTexture(builder.Build(), ISize{0, 0}, aiks_context);
+
+  EXPECT_EQ(texture, nullptr);
+}
+
 }  // namespace testing
 }  // namespace impeller

engine/src/flutter/impeller/display_list/dl_dispatcher.cc

@@ -1309,6 +1309,9 @@ std::shared_ptr<Texture> DisplayListToTexture(
             kDefaultColorAttachmentConfig  // color_attachment_config
     );
   }
+  if (!target.IsValid()) {
+    return nullptr;
+  }
 
   SkIRect sk_cull_rect = SkIRect::MakeWH(size.width, size.height);
   impeller::FirstPassDispatcher collector(

engine/src/flutter/shell/common/snapshot_controller_impeller.cc

@@ -58,7 +58,7 @@ sk_sp<DlImage> DoMakeRasterSnapshot(
     const sk_sp<DisplayList>& display_list,
     SkISize size,
     const SnapshotController::Delegate& delegate) {
-  // Ensure that the current thread has a rendering context.  This must be done
+  // Ensure that the current thread has a rendering context. This must be done
   // before calling GetAiksContext because constructing the AiksContext may
   // invoke graphics APIs.
   std::unique_ptr<Surface> pbuffer_surface;