mix-blend-mode implementation for accelerated layers

cc/quads/render_pass_draw_quad.cc

Index: cc/quads/render_pass_draw_quad.cc
diff --git a/cc/quads/render_pass_draw_quad.cc b/cc/quads/render_pass_draw_quad.cc
index 73b2553e209213b13289d262329db5eaa5449a98..002d61421fcea6c93b1301784387caff3f046d4d 100644
--- a/cc/quads/render_pass_draw_quad.cc
+++ b/cc/quads/render_pass_draw_quad.cc
@@ -14,7 +14,8 @@ namespace cc {
 RenderPassDrawQuad::RenderPassDrawQuad()
     : render_pass_id(RenderPass::Id(-1, -1)),
       is_replica(false),
-      mask_resource_id(-1) {
+      mask_resource_id(-1),
+      blend_mode(SkXfermode::kSrcOver_Mode) {
 }
 
 RenderPassDrawQuad::~RenderPassDrawQuad() {
@@ -44,7 +45,8 @@ void RenderPassDrawQuad::SetNew(
     gfx::RectF mask_uv_rect,
     const FilterOperations& filters,
     skia::RefPtr<SkImageFilter> filter,
-    const FilterOperations& background_filters) {
+    const FilterOperations& background_filters,
+    SkXfermode::Mode blend_mode) {
   DCHECK_GT(render_pass_id.layer_id, 0);
   DCHECK_GE(render_pass_id.index, 0);
 
@@ -54,7 +56,7 @@ void RenderPassDrawQuad::SetNew(
   SetAll(shared_quad_state, rect, opaque_rect, visible_rect, needs_blending,
          render_pass_id, is_replica, mask_resource_id,
          contents_changed_since_last_frame, mask_uv_rect, filters, filter,
-         background_filters);
+         background_filters, blend_mode);
 }
 
 void RenderPassDrawQuad::SetAll(
@@ -70,7 +72,8 @@ void RenderPassDrawQuad::SetAll(
     gfx::RectF mask_uv_rect,
     const FilterOperations& filters,
     skia::RefPtr<SkImageFilter> filter,
-    const FilterOperations& background_filters) {
+    const FilterOperations& background_filters,
+    SkXfermode::Mode blend_mode) {
   DCHECK_GT(render_pass_id.layer_id, 0);
   DCHECK_GE(render_pass_id.index, 0);
 
@@ -84,6 +87,7 @@ void RenderPassDrawQuad::SetAll(
   this->filters = filters;
   this->filter = filter;
   this->background_filters = background_filters;
+  this->blend_mode = blend_mode;
 }
 
 void RenderPassDrawQuad::IterateResources(