Android WebView: clean up the AwContentsClientBridge webcontents userdata.

android_webview/browser/aw_javascript_dialog_manager.cc

Index: android_webview/browser/aw_javascript_dialog_manager.cc
diff --git a/android_webview/browser/aw_javascript_dialog_manager.cc b/android_webview/browser/aw_javascript_dialog_manager.cc
index 630c7bfd7af03df9a97e5f78c64ebcf21fbb755f..476935a53c8068e8db3295c6e211af7f0691e40d 100644
--- a/android_webview/browser/aw_javascript_dialog_manager.cc
+++ b/android_webview/browser/aw_javascript_dialog_manager.cc
@@ -25,6 +25,11 @@ void AwJavaScriptDialogManager::RunJavaScriptDialog(
     bool* did_suppress_message) {
   AwContentsClientBridgeBase* bridge =
       AwContentsClientBridgeBase::FromWebContents(web_contents);
+  if (!bridge) {
+    callback.Run(false, base::string16());
+    return;
+  }
+
   bridge->RunJavaScriptDialog(message_type,
                               origin_url,
                               message_text,
@@ -39,6 +44,11 @@ void AwJavaScriptDialogManager::RunBeforeUnloadDialog(
     const DialogClosedCallback& callback) {
   AwContentsClientBridgeBase* bridge =
       AwContentsClientBridgeBase::FromWebContents(web_contents);
+  if (!bridge) {
+    callback.Run(false, base::string16());
+    return;
+  }
+
   bridge->RunBeforeUnloadDialog(web_contents->GetURL(),
                                 message_text,
                                 callback);