android: Avoid render pass in browser compositor

Setting opacity on a layer with children that draws leads to using a
render pass, which is super expensive. Use the usual trick of setting
opacity on the leaf layers directly instead.

Change-Id: If394f0bba0953b9c6b951d2f320b358fe16c8acb
Reviewed-on: https://chromium-review.googlesource.com/1238566Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593556}

chrome/browser/android/compositor/layer/tab_layer.cc

@@ -489,7 +489,7 @@ void TabLayer::SetProperties(int id,
     transform.Translate(toolbar_position.x(), toolbar_position.y());
     toolbar_layer_->layer()->SetTransformOrigin(gfx::Point3F(0.f, 0.f, 0.f));
     toolbar_layer_->layer()->SetTransform(transform);
-    toolbar_layer_->layer()->SetOpacity(toolbar_alpha);
+    toolbar_layer_->SetOpacity(toolbar_alpha);
 
     toolbar_layer_->layer()->SetMasksToBounds(
         toolbar_layer_->layer()->bounds() != toolbar_size);

chrome/browser/android/compositor/layer/toolbar_layer.cc

@@ -157,6 +157,14 @@ void ToolbarLayer::UpdateProgressBar(int progress_bar_x,
   }
 }
 
+void ToolbarLayer::SetOpacity(float opacity) {
+  toolbar_background_layer_->SetOpacity(opacity);
+  url_bar_background_layer_->SetOpacity(opacity);
+  bitmap_layer_->SetOpacity(opacity);
+  progress_bar_layer_->SetOpacity(opacity);
+  progress_bar_background_layer_->SetOpacity(opacity);
+}
+
 ToolbarLayer::ToolbarLayer(ui::ResourceManager* resource_manager)
     : resource_manager_(resource_manager),
       layer_(cc::Layer::Create()),

chrome/browser/android/compositor/layer/toolbar_layer.h

@@ -51,6 +51,8 @@ class ToolbarLayer : public Layer {
                          int progress_bar_background_height,
                          int progress_bar_background_color);
 
+  void SetOpacity(float opacity);
+
  protected:
   explicit ToolbarLayer(ui::ResourceManager* resource_manager);
   ~ToolbarLayer() override;