don't report GPU image size (#35473)

lib/ui/painting/image.cc

@@ -40,15 +40,9 @@ void CanvasImage::dispose() {
 }
 
 size_t CanvasImage::GetAllocationSize() const {
-  auto size = sizeof(this);
-  if (image_) {
-    size += image_->GetApproximateByteSize();
-  }
-  // The VM will assert if we set a value larger than or close to
-  // std::numeric_limits<intptr_t>::max().
-  // https://github.com/dart-lang/sdk/issues/49332
-  return std::clamp(
-      size, static_cast<size_t>(0),
-      static_cast<size_t>(std::numeric_limits<intptr_t>::max() / 10));
+  // We don't actually want Dart's GC to use the size of this object to make GC
+  // decisions, as it is generally both created and disposed in the framework.
+  // This is similar to why we do not report the sizes of engine layers.
+  return sizeof(*this);
 }
 }  // namespace flutter

lib/ui/painting/image_encoding_unittests.cc

@@ -125,6 +125,7 @@ TEST_F(ShellTest, EncodeImageAccessesSyncSwitch) {
         image_handle, tonic::DartWrappable::kPeerIndex, &peer);
     ASSERT_FALSE(Dart_IsError(result));
     CanvasImage* canvas_image = reinterpret_cast<CanvasImage*>(peer);
+    ASSERT_EQ(canvas_image->GetAllocationSize(), sizeof(*canvas_image));
 
     int64_t format = -1;
     result = Dart_IntegerToInt64(format_handle, &format);