mix-blend-mode implementation for accelerated layers

cc/trees/layer_tree_host_common.cc

Index: cc/trees/layer_tree_host_common.cc
diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index c2b77bd0ff1dab5daca92c288d6f89e036c32f63..db56baf13499e812c52d02cdafe8ba7815fb0a5b 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -575,6 +575,30 @@ static bool SubtreeShouldRenderToSeparateSurface(
     return true;
   }
 
+  // If the layer has blending.
+  // TODO(rosca): this is temporary, until blending is implemented for other
+  // types of quads than RenderPassQuad. Layers having descendants that draw
+  // content will still create a separate rendering surface.
+  if (!layer->uses_default_blend_mode()) {
+      TRACE_EVENT_INSTANT0(
+          "cc",
+          "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface blending",
+          TRACE_EVENT_SCOPE_THREAD);
+      return true;
+  }
+
+  // If the layer has isolation.
+  // TODO(rosca): to be optimized - create separate rendering surface only when
+  // the blending descendants might have access to the content behind this layer
+  // (layer has transparent background or descendants overflow)
+  if (layer->is_root_for_isolated_group()) {
+    TRACE_EVENT_INSTANT0(
+        "cc",
+        "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface isolation",
+        TRACE_EVENT_SCOPE_THREAD);
+    return true;
+  }
+
   // If the layer clips its descendants but it is not axis-aligned with respect
   // to its parent.
   bool layer_clips_external_content =