cc: Make HasImplThread() function work in AfterTest().

cc/test/layer_tree_test.h

Index: cc/test/layer_tree_test.h
diff --git a/cc/test/layer_tree_test.h b/cc/test/layer_tree_test.h
index ffba9e88c2d8026a8bee7e2f5999da6e8dffc91f..15ec2151b83c57480f241ce3d2189946ad998f83 100644
--- a/cc/test/layer_tree_test.h
+++ b/cc/test/layer_tree_test.h
@@ -184,7 +184,7 @@ class LayerTreeTest : public testing::Test, public TestHooks {
                        bool impl_side_painting);
   virtual void RunTestWithImplSidePainting();
 
-  bool HasImplThread() { return proxy() ? proxy()->HasImplThread() : false; }
+  bool HasImplThread() { return !!impl_thread_; }
   base::SingleThreadTaskRunner* ImplThreadTaskRunner() {
     DCHECK(proxy());
     return proxy()->ImplThreadTaskRunner() ? proxy()->ImplThreadTaskRunner()