Protocol handler dialogs should only be enabled by browser or page actions [Not committed]

chrome/browser/extensions/api/extension_action/extension_action_api.cc

Index: chrome/browser/extensions/api/extension_action/extension_action_api.cc
diff --git a/chrome/browser/extensions/api/extension_action/extension_action_api.cc b/chrome/browser/extensions/api/extension_action/extension_action_api.cc
index a7e077566d901ed4502cefc6262dbb1cb1d47f27..13906db27c0f66bc2ee2097be903a316d1377ed8 100644
--- a/chrome/browser/extensions/api/extension_action/extension_action_api.cc
+++ b/chrome/browser/extensions/api/extension_action/extension_action_api.cc
@@ -22,6 +22,7 @@
 #include "chrome/browser/extensions/location_bar_controller.h"
 #include "chrome/browser/extensions/state_store.h"
 #include "chrome/browser/extensions/tab_helper.h"
+#include "chrome/browser/external_protocol/external_protocol_handler.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/extensions/api/extension_action/action_info.h"
 #include "chrome/common/render_messages.h"
@@ -354,7 +355,9 @@ void ExtensionActionAPI::ExtensionActionExecuted(
       // The System Indicator handles its own clicks.
       break;
   }
-
+  // Browser and page actions should enable launching external protocol
+  // handlers in the absence of any other user gesture.
+  ExternalProtocolHandler::PermitLaunchUrl();

[Jeffrey Yasskin, 2014/01/28 00:54:19]

The other place I'd expect people to be relying on a user gesture being
available is in postMessage()s to their extensions. The bottleneck for that in
the browser process looks like MessageService::DispatchMessage() at
https://code.google.com/p/chromium/codesearch/#chromium/src/chrome/browser/ex...,
where you'd check for message.user_gesture. If you can enable this
renderer-side, you can also use  MessagingBindings::DeliverMessage
(https://code.google.com/p/chromium/codesearch/#chromium/src/chrome/renderer/e...).
It's also possible that postMessage already enables external protocol handlers,
since it does get a Blink-side WebScopedUserGesture.

Context menus might also need this: MenuManager::ExecuteCommand at
https://code.google.com/p/chromium/codesearch/#chromium/src/chrome/browser/ex...

[meacer, 2014/01/30 00:20:44]

Just to clarify: If postMessage wasn't called from within a user gesture, it
shouldn't enable protocol handlers, right? Or do you mean developers would
expect postMessage to enable handlers even without a user gesture?
Looks like it doesn't already enable, the WebScopedUserGesture is created in
that method if message.user_gesture is true.
I'll add the enable code into ActiveTabPermissionGranter::GrantIfRequested as it
looks like it's only invoked by user actions. Should cover
MenuManager::ExecuteCommand as well.

   if (event_name) {
     scoped_ptr<base::ListValue> args(new base::ListValue());
     base::DictionaryValue* tab_value =