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

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 0bf40594b49d519a242d450b1859190577331892..7ae1945a2e0514a1330623bdadb1916cb5bd837c 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1613,6 +1613,17 @@ void LayerTreeHostImpl::UpdateGpuRasterizationStatus() {
     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;