Limit extensions to 1 UI surface (either Page/Browser action, but not both)....

chrome/common/extensions/extension.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/common/extensions/extension.h"
 
 #include "app/resource_bundle.h"
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
@@ skipping 940 matching lines @@
 
     page_action_.reset(
         LoadExtensionActionHelper(page_action_value, error,
                                   ExtensionAction::PAGE_ACTION));
     if (!page_action_.get())
       return false;  // Failed to parse page action definition.
   }
 
   // Initialize browser action (optional).
   if (source.HasKey(keys::kBrowserAction)) {
+    // Restrict extensions to one UI surface.
+    if (source.HasKey(keys::kPageAction) || source.HasKey(keys::kPageActions)) {
+      *error = errors::kOneUISurfaceOnly;
+      return false;
+    }
+
     DictionaryValue* browser_action_value;
     if (!source.GetDictionary(keys::kBrowserAction, &browser_action_value)) {
       *error = errors::kInvalidBrowserAction;
       return false;
     }
 
     browser_action_.reset(
         LoadExtensionActionHelper(browser_action_value, error,
                                   ExtensionAction::BROWSER_ACTION));
     if (!browser_action_.get())
@@ skipping 187 matching lines @@
     UserScript::PatternList::const_iterator pattern =
         content_script->url_patterns().begin();
     for (; pattern != content_script->url_patterns().end(); ++pattern) {
       if (pattern->match_subdomains() && pattern->host().empty())
         return true;
     }
   }
 
   return false;
 }