Fix "crashed extension" infobar browser crashes.

chrome/browser/extensions/extension_prefs.h

 // 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_EXTENSION_PREFS_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_PREFS_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 38 matching lines @@
   // Called to change the extension's state when it is enabled/disabled.
   void SetExtensionState(Extension* extension, Extension::State);
 
   // Returns the version string for the currently installed extension, or
   // the empty string if not found.
   std::string GetVersionString(const std::string& extension_id);
 
   // Ensure old extensions have fully up-to-date prefs values.
   void MigrateToPrefs(Extension* extension);
 
+  // Returns extension path based on extension ID, or empty FilePath on error.
+  FilePath GetExtensionPath(const std::string& extension_id);
+
   // Returns base extensions install directory.
   const FilePath& install_directory() const { return install_directory_; }
 
   // Updates the prefs based on the blacklist.
   void UpdateBlacklist(const std::set<std::string>& blacklist_set);
 
   // Based on extension id, checks prefs to see if it is blacklisted.
   bool IsExtensionBlacklisted(const std::string& id);
 
  private:
@@ skipping 57 matching lines @@
  private:
   // A copy of the extensions pref dictionary so that this can be passed
   // around without a dependency on prefs.
   scoped_ptr<DictionaryValue> extension_data_;
 
   DISALLOW_COPY_AND_ASSIGN(InstalledExtensions);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_PREFS_H_