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 bdb537aa6627d34d7be142c772419ce6ce5fe301..93a4114e2b204f9a5454740b94882eebacef8b7b 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -163,7 +163,13 @@ class GLRenderer::ScopedUseGrContext {
  public:
   static scoped_ptr<ScopedUseGrContext> Create(GLRenderer* renderer,
                                                DrawingFrame* frame) {
-    return make_scoped_ptr(new ScopedUseGrContext(renderer, frame));
+    // GrContext for filters is created lazily, and may fail if the context
+    // is lost.
+    // TODO(vmiura,bsalomon): crbug.com/487850 Ensure that
+    // ContextProvider::GrContext() does not return NULL.
+    if (renderer->output_surface_->context_provider()->GrContext())
+      return make_scoped_ptr(new ScopedUseGrContext(renderer, frame));
+    return nullptr;
   }
 
   ~ScopedUseGrContext() {