Remove CompositeAndReadback from LayerTreeHost(Impl) and the Proxys.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index a532baf145ed6295671fae5708861c7a9579dcf5..aa51c93cd74d460df06dd37599d404d46a6f6869 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -107,7 +107,6 @@ LayerTreeHost::LayerTreeHost(LayerTreeHostClient* client,
       page_scale_factor_(1.f),
       min_page_scale_factor_(1.f),
       max_page_scale_factor_(1.f),
-      trigger_idle_updates_(true),
       has_gpu_rasterization_trigger_(false),
       content_is_suitable_for_gpu_rasterization_(true),
       background_color_(SK_ColorWHITE),
@@ -454,15 +453,6 @@ void LayerTreeHost::DidLoseOutputSurface() {
   SetNeedsCommit();
 }
 
-bool LayerTreeHost::CompositeAndReadback(
-    void* pixels,
-    const gfx::Rect& rect_in_device_viewport) {
-  trigger_idle_updates_ = false;
-  bool ret = proxy_->CompositeAndReadback(pixels, rect_in_device_viewport);
-  trigger_idle_updates_ = true;
-  return ret;
-}
-
 void LayerTreeHost::FinishAllRendering() {
   proxy_->FinishAllRendering();
 }
@@ -838,7 +828,7 @@ bool LayerTreeHost::UpdateLayers(Layer* root_layer,
   bool need_more_updates = false;
   PaintLayerContents(
       update_list, queue, &did_paint_content, &need_more_updates);
-  if (trigger_idle_updates_ && need_more_updates) {
+  if (need_more_updates) {
     TRACE_EVENT0("cc", "LayerTreeHost::UpdateLayers::posting prepaint task");
     prepaint_callback_.Reset(base::Bind(&LayerTreeHost::TriggerPrepaint,
                                         base::Unretained(this)));