cc: Don't draw and swap if the frame will not change.

cc/trees/layer_tree_host_unittest_context.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/content_layer.h"
 #include "cc/layers/heads_up_display_layer.h"
 #include "cc/layers/io_surface_layer.h"
@@ skipping 137 matching lines @@
           base::Bind(&LayerTreeHostContextTest::CreateOffscreenContext3d,
                      base::Unretained(this)));
     }
     return offscreen_contexts_compositor_thread_;
   }
 
   virtual bool PrepareToDrawOnThread(LayerTreeHostImpl* host_impl,
                                      LayerTreeHostImpl::FrameData* frame,
                                      bool result)
       OVERRIDE {
-    EXPECT_TRUE(result);
+    bool expect_success = !frame->has_no_damage;
+    EXPECT_EQ(expect_success, result);
     if (!times_to_lose_during_draw_)
       return result;
 
     --times_to_lose_during_draw_;
     context3d_->set_times_make_current_succeeds(0);
 
     times_to_fail_create_ = times_to_fail_recreate_;
     times_to_fail_recreate_ = 0;
     times_to_fail_initialize_ = times_to_fail_reinitialize_;
     times_to_fail_reinitialize_ = 0;
@@ skipping 93 matching lines @@
       return;
 
     recovered_context_ = false;
     if (NextTestCase())
       InvalidateAndSetNeedsCommit();
     else
       EndTest();
   }
 
   virtual void InvalidateAndSetNeedsCommit() {
-    layer_tree_host()->SetNeedsCommit();
+    // Cause damage so we try to draw.
+    layer_tree_host()->root_layer()->SetNeedsDisplay();
   }
 
   bool NextTestCase() {
     static const TestCase kTests[] = {
       // Losing the context and failing to recreate it (or losing it again
       // immediately) a small number of times should succeed.
       { 1,  // times_to_lose_during_commit
         0,  // times_to_lose_during_draw
         3,  // times_to_fail_reinitialize
         0,  // times_to_fail_recreate
@@ skipping 760 matching lines @@
 
     if (host_impl->active_tree()->source_frame_number() == 3) {
       // On the third commit we're recovering from context loss. Hardware
       // video frames should not be reused by the VideoFrameProvider, but
       // software frames can be.
       hw_frame_provider_.set_frame(NULL);
       scaled_hw_frame_provider_.set_frame(NULL);
     }
   }
 
-  virtual bool PrepareToDrawOnThread(
-      LayerTreeHostImpl* host_impl,
-      LayerTreeHostImpl::FrameData* frame,
-      bool result) OVERRIDE {
+  virtual bool PrepareToDrawOnThread(LayerTreeHostImpl* host_impl,
+                                     LayerTreeHostImpl::FrameData* frame,
+                                     bool result) OVERRIDE {
     if (host_impl->active_tree()->source_frame_number() == 2) {
       // Lose the context during draw on the second commit. This will cause
       // a third commit to recover.
       if (context3d_)
         context3d_->set_times_bind_texture_succeeds(4);
     }
     return true;
   }
 
   virtual void DidCommitAndDrawFrame() OVERRIDE {
@@ skipping 153 matching lines @@
 
  private:
   int commits_;
   scoped_refptr<FakeScrollbarLayer> scrollbar_layer_;
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(ScrollbarLayerLostContext);
 
 }  // namespace
 }  // namespace cc