cc: Add null checks for GrContext created by ContextProviderCommandBuffer.

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index 10985875d8c36122453ee585c8d6dc85bad36621..5335ea72fde2d0ff3cb5ac7290fb696779d0a564 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -163,7 +163,10 @@ class GLRenderer::ScopedUseGrContext {
  public:
   static scoped_ptr<ScopedUseGrContext> Create(GLRenderer* renderer,
                                                DrawingFrame* frame) {
-    return make_scoped_ptr(new ScopedUseGrContext(renderer, frame));
+    // GrContext creation may fail.
+    if (renderer->output_surface_->context_provider()->GrContext())
+      return make_scoped_ptr(new ScopedUseGrContext(renderer, frame));
+    return nullptr;
   }
 
   ~ScopedUseGrContext() {