Report size estimates to Dart for Image/Picture/Paragraph objects (#3840)

Fixes https://github.com/flutter/flutter/issues/11007

lib/ui/painting/image.cc

@@ -40,4 +40,12 @@ void CanvasImage::dispose() {
   ClearDartWrapper();
 }
 
+size_t CanvasImage::GetAllocationSize() {
+  if (image_) {
+    return image_->width() * image_->height() * 4;
+  } else {
+    return sizeof(CanvasImage);
+  }
+}
+
 }  // namespace blink

lib/ui/painting/image.h

@@ -32,6 +32,8 @@ class CanvasImage final : public ftl::RefCountedThreadSafe<CanvasImage>,
   const sk_sp<SkImage>& image() const { return image_; }
   void set_image(sk_sp<SkImage> image) { image_ = std::move(image); }
 
+  virtual size_t GetAllocationSize() override;
+
   static void RegisterNatives(tonic::DartLibraryNatives* natives);
 
  private:

lib/ui/painting/picture.cc

@@ -48,4 +48,12 @@ void Picture::dispose() {
   ClearDartWrapper();
 }
 
+size_t Picture::GetAllocationSize() {
+  if (picture_) {
+    return picture_->approximateBytesUsed();
+  } else {
+    return sizeof(Picture);
+  }
+}
+
 }  // namespace blink

lib/ui/painting/picture.h

@@ -31,6 +31,8 @@ class Picture : public ftl::RefCountedThreadSafe<Picture>,
 
   void dispose();
 
+  virtual size_t GetAllocationSize() override;
+
   static void RegisterNatives(tonic::DartLibraryNatives* natives);
 
  private:

lib/ui/text/paragraph.cc

@@ -51,6 +51,13 @@ Paragraph::~Paragraph() {
   }
 }
 
+size_t Paragraph::GetAllocationSize() {
+  // We don't have an accurate accounting of the paragraph's memory consumption,
+  // so return a fixed size to indicate that its impact is more than the size
+  // of the Paragraph class.
+  return 2000;
+}
+
 double Paragraph::width() {
   return firstChildBox()->width();
 }

lib/ui/text/paragraph.h

@@ -45,6 +45,8 @@ class Paragraph : public ftl::RefCountedThreadSafe<Paragraph>,
 
   RenderView* renderView() const { return m_renderView.get(); }
 
+  virtual size_t GetAllocationSize() override;
+
   static void RegisterNatives(tonic::DartLibraryNatives* natives);
 
  private: