Match html canvas which is transferred to OffscreenCanvas to CSS style

cc/layers/surface_layer_impl.cc

Index: cc/layers/surface_layer_impl.cc
diff --git a/cc/layers/surface_layer_impl.cc b/cc/layers/surface_layer_impl.cc
index 2289a29326f449746f68eb7ddff19fd3a0ba58bf..3f35e78ace14d1066b519d1c52317c8b25e3b3bd 100644
--- a/cc/layers/surface_layer_impl.cc
+++ b/cc/layers/surface_layer_impl.cc
@@ -16,7 +16,9 @@
 namespace cc {
 
 SurfaceLayerImpl::SurfaceLayerImpl(LayerTreeImpl* tree_impl, int id)
-    : LayerImpl(tree_impl, id), surface_scale_(0.f) {
+    : LayerImpl(tree_impl, id),
+      surface_scale_(0.f),

[danakj, 2016/11/28 22:26:22]

can you move both of these to the .h

[xlai (Olivia), 2016/12/13 17:29:18]

Done.

+      scale_layer_bounds_with_surface_size_(false) {
   layer_tree_impl()->AddSurfaceLayer(this);
 }
 
@@ -53,6 +55,14 @@ void SurfaceLayerImpl::SetSurfaceSize(const gfx::Size& size) {
   NoteLayerPropertyChanged();
 }
 
+void SurfaceLayerImpl::SetScaleLayerBoundsWithSurfaceSize(
+    bool is_scaling_needed) {
+  if (scale_layer_bounds_with_surface_size_ == is_scaling_needed)
+    return;
+
+  scale_layer_bounds_with_surface_size_ = is_scaling_needed;

[danakj, 2016/11/28 22:26:22]

You should NoteLayerPropertyChanged() when something changes that affects how
the layer's contents are drawn. Also otherwise we might not pushproperties on
the layer, so you'd have to notify that push props is needed otherwise.

[xlai (Olivia), 2016/12/13 17:29:18]

Done.

+}
+
 void SurfaceLayerImpl::PushPropertiesTo(LayerImpl* layer) {
   LayerImpl::PushPropertiesTo(layer);
   SurfaceLayerImpl* layer_impl = static_cast<SurfaceLayerImpl*>(layer);
@@ -60,6 +70,8 @@ void SurfaceLayerImpl::PushPropertiesTo(LayerImpl* layer) {
   layer_impl->SetSurfaceId(surface_id_);
   layer_impl->SetSurfaceSize(surface_size_);
   layer_impl->SetSurfaceScale(surface_scale_);
+  layer_impl->SetScaleLayerBoundsWithSurfaceSize(
+      scale_layer_bounds_with_surface_size_);
 }
 
 void SurfaceLayerImpl::AppendQuads(RenderPass* render_pass,
@@ -68,7 +80,18 @@ void SurfaceLayerImpl::AppendQuads(RenderPass* render_pass,
 
   SharedQuadState* shared_quad_state =
       render_pass->CreateAndAppendSharedQuadState();
-  PopulateScaledSharedQuadState(shared_quad_state, surface_scale_);
+
+  if (scale_layer_bounds_with_surface_size_) {
+    // When a DOM element's size in CSS style is changed and it is using

[danakj, 2016/11/28 22:26:22]

DOM and CSS are foreign concepts to cc/ so can you rewrite this without using
blink terminology? Just speak in terms of layers and surface content.

[xlai (Olivia), 2016/12/13 17:29:18]

Done.

+    // SurfaceLayer, it is possible that its layer bounds and surface_size
+    // are changed differently on width and height. In this case, we apply a
+    // corresponding transform on the shared_quad_state.
+    float scale_x = ((float)surface_size_.width()) / bounds().width();

[danakj, 2016/11/28 22:26:22]

static_cast, not c-style cast

[xlai (Olivia), 2016/12/13 17:29:18]

Done.

+    float scale_y = ((float)surface_size_.height()) / bounds().height();
+    PopulateScaledSharedQuadState(shared_quad_state, scale_x, scale_y);
+  } else {
+    PopulateScaledSharedQuadState(shared_quad_state, surface_scale_);
+  }
 
   if (!surface_id_.is_valid())
     return;
@@ -77,6 +100,7 @@ void SurfaceLayerImpl::AppendQuads(RenderPass* render_pass,
   gfx::Rect visible_quad_rect =
       draw_properties().occlusion_in_content_space.GetUnoccludedContentRect(
           quad_rect);
+
   if (visible_quad_rect.IsEmpty())
     return;
   SurfaceDrawQuad* quad =