Don't leave renderer process frozen when canceling JavaScript dialogs.

chrome/browser/ui/app_modal_dialogs/javascript_app_modal_dialog.cc

Index: chrome/browser/ui/app_modal_dialogs/javascript_app_modal_dialog.cc
diff --git a/chrome/browser/ui/app_modal_dialogs/javascript_app_modal_dialog.cc b/chrome/browser/ui/app_modal_dialogs/javascript_app_modal_dialog.cc
index c65a732ceba0cf96993196f6b6f54fb912404664..758d79e1b5cb678f8f8b0b50c6c08e30c9fcf727 100644
--- a/chrome/browser/ui/app_modal_dialogs/javascript_app_modal_dialog.cc
+++ b/chrome/browser/ui/app_modal_dialogs/javascript_app_modal_dialog.cc
@@ -108,7 +108,10 @@ void JavaScriptAppModalDialog::Invalidate() {
     return;
 
   AppModalDialog::Invalidate();
-  callback_.Reset();
+  if (!callback_.is_null()) {
+    callback_.Run(false, string16());
+    callback_.Reset();
+  }
   if (native_dialog())
     CloseModalDialog();
 }
@@ -161,7 +164,10 @@ void JavaScriptAppModalDialog::NotifyDelegate(bool success,
   if (!IsValid())
     return;
 
-  callback_.Run(success, user_input);
+  if (!callback_.is_null()) {
+    callback_.Run(success, user_input);
+    callback_.Reset();
+  }
 
   // The callback_ above may delete web_contents_, thus removing the extra
   // data from the map owned by ChromeJavaScriptDialogManager. Make sure