Reduce boilerplate when creating simple mojom::URLLoaders.

content/common/resource_request_completion_status.h

Index: content/common/resource_request_completion_status.h
diff --git a/content/common/resource_request_completion_status.h b/content/common/resource_request_completion_status.h
index 594119a82a6be88f9a20e4bdc903f3b15fe5046e..073704e269484eae420151a5846717904430388e 100644
--- a/content/common/resource_request_completion_status.h
+++ b/content/common/resource_request_completion_status.h
@@ -17,6 +17,9 @@ struct CONTENT_EXPORT ResourceRequestCompletionStatus {
   ResourceRequestCompletionStatus();
   ResourceRequestCompletionStatus(
       const ResourceRequestCompletionStatus& status);
+  explicit ResourceRequestCompletionStatus(int64_t length);
+  // Sets error_code to net::OK, completition_time to base::TimeTicks::Now(),
+  // and encoded_data_length = encoded_body_length = |length|;
   ~ResourceRequestCompletionStatus();
 
   // The error code.