cc: Adding BeginFrameTracker object and removing Now() from LTHI.

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index b536173401026ab27df223f4198b2642cd132a8d..3a83c86a6320dbb39a6620e16f0fd5b2ffae0942 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -171,6 +171,9 @@ class LayerTreeHostImplTest : public testing::Test,
                                            0);
     bool init = host_impl_->InitializeRenderer(output_surface.Pass());
     host_impl_->SetViewportSize(gfx::Size(10, 10));
+    // Set the BeginFrameArgs so that methods which use it are able to.
+    host_impl_->WillBeginImplFrame(
+        CreateBeginFrameArgsForTesting(BEGINFRAME_FROM_HERE));
     return init;
   }