Fix DCHECK(gr_texture) when running test_sky

sky/compositor/layer_host.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/compositor/layer_host.h"
 
 #include "base/debug/trace_event.h"
 #include "base/message_loop/message_loop.h"
 #include "mojo/converters/geometry/geometry_type_converters.h"
 #include "mojo/gpu/gl_context.h"
@@ skipping 57 matching lines @@
   TRACE_EVENT0("sky", "LayerHost::BeginFrame");
 
   DCHECK(frame_requested_);
   frame_requested_ = false;
 
   DCHECK_EQ(state_, kReadyForFrame);
   state_ = kWaitingForFrameAcknowldgement;
 
   client_->BeginFrame(base::TimeTicks::Now());
 
+  // If the root layer is empty, there's no reason to draw into it. (In fact,
+  // Ganesh will get upset if we try.) Instead, we just schedule the ack that
+  // the frame is complete.
+  if (root_layer_->size().IsEmpty()) {
+    base::MessageLoop::current()->PostTask(
+        FROM_HERE,
+        base::Bind(&LayerHost::DidCompleteFrame, weak_factory_.GetWeakPtr()));
+    return;
+  }
+
   {
     mojo::GaneshContext::Scope scope(&ganesh_context_);
     ganesh_context_.gr()->resetContext();
     root_layer_->Display();
   }
 
   Upload(root_layer_.get());
 }
 
 void LayerHost::Upload(Layer* layer) {
@@ skipping 52 matching lines @@
 }
 
 void LayerHost::DidCompleteFrame() {
   DCHECK_EQ(state_, kWaitingForFrameAcknowldgement);
   state_ = kReadyForFrame;
   if (frame_requested_)
     BeginFrame();
 }
 
 }  // namespace sky