Re-land: exo: Take blending into account when setting opaque property.

This makes SetFillsBoundsOpaquely() call consistent with opaque_rect
used in UpdateSurface() when creating a texture quad.

BUG=549781

Review-Url: https://codereview.chromium.org/2101453002
Cr-Commit-Position: refs/heads/master@{#402648}

components/exo/surface.cc

@@ -485,8 +485,7 @@ void Surface::CommitSurfaceHierarchy() {
     window_->layer()->SetBounds(
         gfx::Rect(window_->layer()->bounds().origin(), content_size_));
     window_->layer()->SetFillsBoundsOpaquely(
-        state_.alpha == 1.0f &&
-
+        state_.blend_mode == SkXfermode::kSrc_Mode ||
         state_.opaque_region.contains(
             gfx::RectToSkIRect(gfx::Rect(content_size_))));
   }

components/exo/surface_unittest.cc

@@ -206,8 +206,6 @@ TEST_F(SurfaceTest, SetBlendMode) {
   surface->SetBlendMode(SkXfermode::kSrc_Mode);
   surface->Commit();
 
-  EXPECT_FALSE(surface->window()->layer()->fills_bounds_opaquely());
-
   const cc::DelegatedFrameData* frame_data = GetFrameFromSurface(surface.get());
   ASSERT_EQ(1u, frame_data->render_pass_list.size());
   ASSERT_EQ(1u, frame_data->render_pass_list.back()->quad_list.size());