Avoid issuing a Read() after draining a request.

content/browser/loader/resource_handler.h

Index: content/browser/loader/resource_handler.h
diff --git a/content/browser/loader/resource_handler.h b/content/browser/loader/resource_handler.h
index 0b942bbe3657c45e34ed87f9d1dc43a6f95a431e..ded3a350e9071dbddd6af5022f68fb0adddcd8e1 100644
--- a/content/browser/loader/resource_handler.h
+++ b/content/browser/loader/resource_handler.h
@@ -97,7 +97,8 @@ class CONTENT_EXPORT ResourceHandler
   // Data (*bytes_read bytes) was written into the buffer provided by
   // OnWillRead.  A return value of false cancels the request, true continues
   // reading data.  Set |*defer| to true to defer reading more response data.
-  // Call controller()->Resume() to continue reading response data.
+  // Call controller()->Resume() to continue reading response data.  A zero
+  // |bytes_read| signals that no further data is available.
   virtual bool OnReadCompleted(int request_id, int bytes_read,
                                bool* defer) = 0;