Remove unused field draws_content_ from WebContentLayerImpl.

CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1466883003

Cr-Commit-Position: refs/heads/master@{#361050}

cc/blink/web_content_layer_impl.h

@@ -42,7 +42,6 @@ class WebContentLayerImpl : public blink::WebContentLayer,
 
   scoped_ptr<WebLayerImpl> layer_;
   blink::WebContentLayerClient* client_;
-  bool draws_content_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(WebContentLayerImpl);