Adding blend mode to DrawProperties

cc/layers/draw_properties.h

Index: cc/layers/draw_properties.h
diff --git a/cc/layers/draw_properties.h b/cc/layers/draw_properties.h
index 4bbce727deff70f122c131dad21a4b756a01d72c..9fa40527c6811b9a400926bc093f36c8c608e76a 100644
--- a/cc/layers/draw_properties.h
+++ b/cc/layers/draw_properties.h
@@ -6,6 +6,7 @@
 #define CC_LAYERS_DRAW_PROPERTIES_H_
 
 #include "base/memory/scoped_ptr.h"
+#include "third_party/skia/include/core/SkXfermode.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/transform.h"
 
@@ -18,6 +19,7 @@ struct CC_EXPORT DrawProperties {
   DrawProperties()
       : opacity(0.f),
         opacity_is_animating(false),
+        blend_mode(SkXfermode::kSrcOver_Mode),
         screen_space_opacity_is_animating(false),
         target_space_transform_is_animating(false),
         screen_space_transform_is_animating(false),
@@ -58,6 +60,12 @@ struct CC_EXPORT DrawProperties {
   // animating, the main thread may not have the same values that are used
   // to draw.
   bool opacity_is_animating;
+
+  // DrawProperties::blend_mode may be different than LayerType::blend_mode,
+  // particularly in the case when the LayerType has it own RenderSurface which
+  // will take the responsibility to blend the entire subtree.
+  SkXfermode::Mode blend_mode;
+
   bool screen_space_opacity_is_animating;
   bool target_space_transform_is_animating;
   bool screen_space_transform_is_animating;