[Android] Use resource throttle instead of HandleExternalProtocol.

android_webview/browser/renderer_host/aw_resource_dispatcher_host_delegate.cc

Index: android_webview/browser/renderer_host/aw_resource_dispatcher_host_delegate.cc
diff --git a/android_webview/browser/renderer_host/aw_resource_dispatcher_host_delegate.cc b/android_webview/browser/renderer_host/aw_resource_dispatcher_host_delegate.cc
index b0f8e9a5c8a2539a7da35b8df44a09eb8183ae23..387c3b904f9203ed27b196999377ff248319ead6 100644
--- a/android_webview/browser/renderer_host/aw_resource_dispatcher_host_delegate.cc
+++ b/android_webview/browser/renderer_host/aw_resource_dispatcher_host_delegate.cc
@@ -115,12 +115,13 @@ content::ResourceDispatcherHostLoginDelegate*
   return new AwLoginDelegate(auth_info, request);
 }
 
-void AwResourceDispatcherHostDelegate::HandleExternalProtocol(const GURL& url,
+bool AwResourceDispatcherHostDelegate::HandleExternalProtocol(const GURL& url,
                                                               int child_id,
                                                               int route_id) {
   // The AwURLRequestJobFactory implementation should ensure this method never
   // gets called.
   NOTREACHED();
+  return false;
 }
 
 void AwResourceDispatcherHostDelegate::SetOnlyAllowLoadFromCache(