mix-blend-mode implementation for accelerated layers

cc/layers/delegated_renderer_layer.cc

Index: cc/layers/delegated_renderer_layer.cc
diff --git a/cc/layers/delegated_renderer_layer.cc b/cc/layers/delegated_renderer_layer.cc
index a92b70106deefab1a3b5872cda4204442a24b8f2..4cc0bf86ba4fdf55abcf7e5f3d65c371110daaae 100644
--- a/cc/layers/delegated_renderer_layer.cc
+++ b/cc/layers/delegated_renderer_layer.cc
@@ -107,7 +107,7 @@ void DelegatedRendererLayer::SetDisplaySize(gfx::Size size) {
   SetNeedsCommit();
 }
 
-static bool FrameDataHasFilter(DelegatedFrameData* frame) {
+static bool FrameDataRequiresOffscreenContext(const DelegatedFrameData* frame) {
   for (size_t i = 0; i < frame->render_pass_list.size(); ++i) {
     const QuadList& quad_list = frame->render_pass_list[i]->quad_list;
     for (size_t j = 0; j < quad_list.size(); ++j) {
@@ -116,7 +116,9 @@ static bool FrameDataHasFilter(DelegatedFrameData* frame) {
       const RenderPassDrawQuad* render_pass_quad =
           RenderPassDrawQuad::MaterialCast(quad_list[j]);
       if (!render_pass_quad->filters.IsEmpty() ||
-          !render_pass_quad->background_filters.IsEmpty())
+          !render_pass_quad->background_filters.IsEmpty() ||
+          render_pass_quad->shared_quad_state->blend_mode !=
+              SkXfermode::kSrcOver_Mode)
         return true;
     }
   }
@@ -135,7 +137,8 @@ bool DelegatedRendererLayer::Update(ResourceUpdateQueue* queue,
 
   // If any quad has a filter operation, then we need a filter context to draw
   // this layer's content.
-  if (FrameDataHasFilter(frame_data_) && layer_tree_host())
+  if (layer_tree_host() && !layer_tree_host()->needs_offscreen_context() &&
+      FrameDataRequiresOffscreenContext(frame_data_))
     layer_tree_host()->set_needs_filter_context();
 
   return true;