Reland r206537 - cc: Don't return mailboxes if the TextureLayer is removed from the tree.

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 021265bfa54281246c66ab40616559d1a814d9b3..d6201fadb052ea23e9c88ff5640eb63c3bd311d3 100644
--- a/cc/layers/texture_layer_unittest.cc
+++ b/cc/layers/texture_layer_unittest.cc
@@ -413,6 +413,27 @@ class TextureLayerImplWithMailboxThreadedCallback : public LayerTreeTest {
         break;
       case 7:
         EXPECT_EQ(4, callback_count_);
+        // Restore a mailbox for the next step.
+        SetMailbox('5');
+        break;
+      case 8:
+        // Case #5: remove layer from tree. Callback should *not* be called, the
+        // mailbox is returned to the main thread.
+        EXPECT_EQ(4, callback_count_);
+        layer_->RemoveFromParent();
+        break;
+      case 9:
+        // Mailbox was released to the main thread, task was posted, but won't
+        // execute until this DidCommit returns.
+        // TODO(piman): fix this.
+        EXPECT_EQ(4, callback_count_);
+        layer_tree_host()->SetNeedsCommit();
+        break;
+      case 10:
+        EXPECT_EQ(4, callback_count_);
+        // Resetting the mailbox will call the callback now.
+        layer_->SetTextureMailbox(TextureMailbox());
+        EXPECT_EQ(5, callback_count_);
         EndTest();
         break;
       default: