cc: Make PrepareToDraw return an enum for why it aborts

cc/trees/layer_tree_host_unittest_video.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include "base/basictypes.h"
 #include "cc/layers/render_surface_impl.h"
 #include "cc/layers/video_layer.h"
 #include "cc/layers/video_layer_impl.h"
@@ skipping 28 matching lines @@
     layer_tree_host()->SetRootLayer(root);
     layer_tree_host()->SetDeviceScaleFactor(2.f);
     LayerTreeHostVideoTest::SetupTree();
   }
 
   virtual void BeginTest() OVERRIDE {
     num_draws_ = 0;
     PostSetNeedsCommitToMainThread();
   }
 
-  virtual bool PrepareToDrawOnThread(LayerTreeHostImpl* host_impl,
-                                     LayerTreeHostImpl::FrameData* frame,
-                                     bool result) OVERRIDE {
+  virtual DrawSwapReadbackResult::DrawResult PrepareToDrawOnThread(
+      LayerTreeHostImpl* host_impl,
+      LayerTreeHostImpl::FrameData* frame,
+      DrawSwapReadbackResult::DrawResult draw_result) OVERRIDE {
     LayerImpl* root_layer = host_impl->active_tree()->root_layer();
     RenderSurfaceImpl* root_surface = root_layer->render_surface();
     gfx::RectF damage_rect =
         root_surface->damage_tracker()->current_damage_rect();
 
     switch (num_draws_) {
       case 0:
         // First frame the whole viewport is damaged.
         EXPECT_EQ(gfx::RectF(0.f, 0.f, 20.f, 20.f).ToString(),
                   damage_rect.ToString());
         break;
       case 1:
         // Second frame the video layer is damaged.
         EXPECT_EQ(gfx::RectF(6.f, 6.f, 8.f, 8.f).ToString(),
                   damage_rect.ToString());
         EndTest();
         break;
     }
 
-    EXPECT_TRUE(result);
-    return result;
+    EXPECT_EQ(DrawSwapReadbackResult::DID_DRAW, draw_result);
+    return draw_result;
   }
 
   virtual void DrawLayersOnThread(LayerTreeHostImpl* host_impl) OVERRIDE {
     VideoLayerImpl* video = static_cast<VideoLayerImpl*>(
         host_impl->active_tree()->root_layer()->children()[0]);
 
     if (num_draws_ == 0)
       video->SetNeedsRedraw();
 
     ++num_draws_;
   }
 
   virtual void AfterTest() OVERRIDE {
     EXPECT_EQ(2, num_draws_);
   }
 
  private:
   int num_draws_;
 
   FakeVideoFrameProvider video_frame_provider_;
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(LayerTreeHostVideoTestSetNeedsDisplay);
 
 }  // namespace
 }  // namespace cc