cc: Validate that GPU rasterization is usable in UpdateGpuRasterizationStatus().

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <set>
@@ skipping 1595 matching lines @@
   } else if (content_is_suitable_for_gpu_rasterization_) {
     use_gpu = true;
     gpu_rasterization_status_ = GpuRasterizationStatus::ON;
   } else if (using_msaa_for_complex_content) {
     use_gpu = use_msaa = true;
     gpu_rasterization_status_ = GpuRasterizationStatus::MSAA_CONTENT;
   } else {
     gpu_rasterization_status_ = GpuRasterizationStatus::OFF_CONTENT;
   }
 
+  if (use_gpu) {

[danakj, 2015/05/13 20:47:49]

I think this is better than making InitializeRenderer() return false (that would
cause DCHECK in the browser compositor FWIW), and this will still go well with
senorblanco's splitting of the method up still (which I think is nice for better
ordering anyhow).

+    // Ensure that a GrContext is initialized for GPU rasterization.
+    if (!output_surface_->context_provider() ||
+        !output_surface_->worker_context_provider() ||
+        !output_surface_->worker_context_provider()->GrContext()) {
+      use_gpu = false;
+      use_msaa = false;
+      gpu_rasterization_status_ = GpuRasterizationStatus::OFF_DEVICE;
+    }
+  }
+
   if (use_gpu == use_gpu_rasterization_ && use_msaa == use_msaa_)
     return;
 
   // Note that this must happen first, in case the rest of the calls want to
   // query the new state of |use_gpu_rasterization_|.
   use_gpu_rasterization_ = use_gpu;
   use_msaa_ = use_msaa;
 
   // Clean up and replace existing tile manager with another one that uses
   // appropriate rasterizer.
@@ skipping 1773 matching lines @@
   new_target.SetToMin(layer_impl->MaxScrollOffset());
 
   curve->UpdateTarget(
       animation->TrimTimeToCurrentIteration(CurrentBeginFrameArgs().frame_time)
           .InSecondsF(),
       new_target);
 
   return true;
 }
 }  // namespace cc