cc: Allow pepper to avoid DCHECK but reuse gpu::Mailbox.

cc/layers/texture_layer_unittest.cc

Index: cc/layers/texture_layer_unittest.cc
diff --git a/cc/layers/texture_layer_unittest.cc b/cc/layers/texture_layer_unittest.cc
index 88ff0409615523770fd3c0d49ae6b1b513de8f4b..73c6f7325ca87d278b1c03423138f6ddc4a4fa26 100644
--- a/cc/layers/texture_layer_unittest.cc
+++ b/cc/layers/texture_layer_unittest.cc
@@ -459,6 +459,33 @@ TEST_F(TextureLayerWithMailboxTest, ReplaceMailboxOnMainThreadBeforeCommit) {
       SingleReleaseCallback::Create(test_data_.release_mailbox1_));
 }
 
+TEST_F(TextureLayerTest, SetTextureMailboxWithoutReleaseCallback) {
+  scoped_refptr<TextureLayer> test_layer = TextureLayer::CreateForMailbox(NULL);
+  ASSERT_TRUE(test_layer.get());
+
+  // These use the same gpu::Mailbox, but different sync points.
+  TextureMailbox mailbox1(MailboxFromChar('a'), GL_TEXTURE_2D, 1);
+  TextureMailbox mailbox2(MailboxFromChar('a'), GL_TEXTURE_2D, 2);
+
+  EXPECT_CALL(*layer_tree_host_, AcquireLayerTextures()).Times(0);
+  EXPECT_CALL(*layer_tree_host_, SetNeedsCommit()).Times(AnyNumber());
+  layer_tree_host_->SetRootLayer(test_layer);
+  Mock::VerifyAndClearExpectations(layer_tree_host_.get());
+
+  // Set the mailbox the first time. It should cause a commit.
+  EXPECT_CALL(*layer_tree_host_, AcquireLayerTextures()).Times(0);
+  EXPECT_CALL(*layer_tree_host_, SetNeedsCommit()).Times(AtLeast(1));
+  test_layer->SetTextureMailboxWithoutReleaseCallback(mailbox1);
+  Mock::VerifyAndClearExpectations(layer_tree_host_.get());
+
+  // Set the mailbox again with a new sync point, as the backing texture has
+  // been updated. It should cause a new commit.
+  EXPECT_CALL(*layer_tree_host_, AcquireLayerTextures()).Times(0);
+  EXPECT_CALL(*layer_tree_host_, SetNeedsCommit()).Times(AtLeast(1));
+  test_layer->SetTextureMailboxWithoutReleaseCallback(mailbox2);
+  Mock::VerifyAndClearExpectations(layer_tree_host_.get());
+}
+
 class TextureLayerMailboxHolderTest : public TextureLayerTest {
  public:
   TextureLayerMailboxHolderTest()