Fix according to Jim's comments

Author: liyuqian

flow/layers/container_layer.cc

@@ -65,6 +65,13 @@ void ContainerLayer::PaintChildren(PaintContext& context) const {
   }
 }
 
+void ContainerLayer::TryToPrepareRasterCache(PrerollContext* context, Layer* layer, const SkMatrix& matrix) {
+  if (!context->has_platform_view && context->raster_cache &&
+      SkRect::Intersects(context->cull_rect, layer->paint_bounds())) {
+    context->raster_cache->Prepare(context, layer, matrix);
+  }
+}
+
 #if defined(OS_FUCHSIA)
 
 void ContainerLayer::UpdateScene(SceneUpdateContext& context) {

flow/layers/container_layer.h

@@ -37,6 +37,18 @@ class ContainerLayer : public Layer {
   // For OpacityLayer to restructure to have a single child.
   void ClearChildren() { layers_.clear(); }
 
+  // Try to prepare the raster cache for a given layer.
+  //
+  // The raster cache would fail if either of the followings is true:
+  // 1. The context has a platform view.
+  // 2. The context does not have a valid raster cache.
+  // 3. The layer's paint bounds does not intersect with the cull rect.
+  //
+  // We make this a static function instead of a member function that directy
+  // uses the "this" pointer as the layer because we sometimes need to raster
+  // cache a child layer and one can't access its child's protected method.
+  static void TryToPrepareRasterCache(PrerollContext* context, Layer* layer, const SkMatrix& matrix);
+
  private:
   std::vector<std::shared_ptr<Layer>> layers_;
 

flow/layers/image_filter_layer.cc

@@ -28,11 +28,7 @@ void ImageFilterLayer::Preroll(PrerollContext* context,
     set_paint_bounds(child_paint_bounds_);
   }
 
-  if (!context->has_platform_view && context->raster_cache &&
-      SkRect::Intersects(context->cull_rect, paint_bounds())) {
-    SkMatrix ctm = matrix;
-    context->raster_cache->Prepare(context, this, ctm);
-  }
+  TryToPrepareRasterCache(context, this, matrix);
 }
 
 void ImageFilterLayer::Paint(PaintContext& context) const {

flow/layers/opacity_layer.cc

@@ -48,11 +48,7 @@ void OpacityLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
 
   {
     set_paint_bounds(paint_bounds().makeOffset(offset_.fX, offset_.fY));
-    if (!context->has_platform_view && context->raster_cache &&
-        SkRect::Intersects(context->cull_rect, paint_bounds())) {
-      SkMatrix ctm = child_matrix;
-      context->raster_cache->Prepare(context, container, ctm);
-    }
+    TryToPrepareRasterCache(context, container, child_matrix);
   }
 }
 

flow/raster_cache_unittests.cc

@@ -159,9 +159,6 @@ TEST(RasterCache, DeviceRectRoundOut) {
   ASSERT_TRUE(cache.Draw(*picture, canvas));
 
   canvas.translate(248, 0);
-#ifndef SUPPORT_FRACTIONAL_TRANSLATION
-  canvas.setMatrix(RasterCache::GetIntegralTransCTM(canvas.getTotalMatrix()));
-#endif
   ASSERT_TRUE(cache.Draw(*picture, canvas));
 }