[Extensions] Update ExtensionService references in c/b/renderer_context_menu

Update references to ExtensionService in c/b/renderer_context_menu to
use extensions::ExtensionService.

There should be no behavior change as a result of this CL.

Bug: 117261
Change-Id: I7a137ee97d0d884d36cf20db1c8484bae6e5c62a
Reviewed-on: https://chromium-review.googlesource.com/1079716
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#563074}

chrome/browser/renderer_context_menu/render_view_context_menu.cc

@@ -642,7 +642,7 @@ bool RenderViewContextMenu::MenuItemMatchesParams(
 
 void RenderViewContextMenu::AppendAllExtensionItems() {
   extension_items_.Clear();
-  ExtensionService* service =
+  extensions::ExtensionService* service =
       extensions::ExtensionSystem::Get(browser_context_)->extension_service();
   if (!service)
     return;  // In unit-tests, we may not have an ExtensionService.