Disable modal JavaScript dialogs for platform apps.

chrome/browser/extensions/extension_host.cc

Index: chrome/browser/extensions/extension_host.cc
diff --git a/chrome/browser/extensions/extension_host.cc b/chrome/browser/extensions/extension_host.cc
index 1e500bd18609ec585717444260ab48451b9abacd..c6914ead0f0de81ac1af67fb8fd0b760efb5f4b4 100644
--- a/chrome/browser/extensions/extension_host.cc
+++ b/chrome/browser/extensions/extension_host.cc
@@ -400,6 +400,10 @@ void ExtensionHost::CloseContents(WebContents* contents) {
   }
 }
 
+bool ExtensionHost::ShouldSuppressDialogs() {
+  return extension_->is_platform_app();
+}
+
 WebContents* ExtensionHost::OpenURLFromTab(WebContents* source,
                                            const OpenURLParams& params) {
   // Whitelist the dispositions we will allow to be opened.