Move context-related callbacks into OutputSurface

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 7b0a7e12cecbcf8304a840e1493d8237dc6c9aa7..33b5fd994836f7891c746b10d8178a8b1a7c2c53 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1147,7 +1147,11 @@ const LayerTreeSettings& LayerTreeHostImpl::Settings() const {
 }
 
 void LayerTreeHostImpl::DidLoseOutputSurface() {
-  client_->DidLoseOutputSurfaceOnImplThread();
+  // TODO(jamesr): The renderer_ check is needed to make some of the
+  // LayerTreeHostContextTest tests pass, but shouldn't be necessary (or
+  // important) in production. We should adjust the test to not need this.
+  if (renderer_)
+    client_->DidLoseOutputSurfaceOnImplThread();
 }
 
 void LayerTreeHostImpl::OnSwapBuffersComplete() {