[Extensions] Handle some funny cases in script injection

extensions/browser/script_execution_observer.h

 // Copyright 2014 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.
 
 #ifndef EXTENSIONS_BROWSER_SCRIPT_EXECUTION_OBSERVER_H_
 #define EXTENSIONS_BROWSER_SCRIPT_EXECUTION_OBSERVER_H_
 
 #include <map>
 #include <set>
 #include <string>
 
 class GURL;
 
 namespace content {
 class WebContents;
 }
 
 namespace extensions {
 
 // Observer base class for classes that need to be notified when content
 // scripts and/or tabs.executeScript calls run on a page.
 class ScriptExecutionObserver {
  public:
   // Map of extensions IDs to the executing script paths.
   typedef std::map<std::string, std::set<std::string> > ExecutingScriptsMap;
 
   // Called when script(s) have executed on a page.
   //
   // |executing_scripts_map| contains all extensions that are executing
-  // scripts, mapped to the paths for those scripts. This may be an empty set
-  // if the script has no path associated with it (e.g. in the case of
-  // tabs.executeScript).
+  // scripts, mapped to the paths for those scripts. The paths may be an empty
+  // set if the script has no path associated with it (e.g. in the case of
+  // tabs.executeScript), but there will still be an entry for the extension.
   virtual void OnScriptsExecuted(
       const content::WebContents* web_contents,
       const ExecutingScriptsMap& executing_scripts_map,
       const GURL& on_url) = 0;
 
  protected:
   virtual ~ScriptExecutionObserver();
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_SCRIPT_EXECUTION_OBSERVER_H_