Fix "crashed extension" infobar browser crashes.

chrome/browser/extensions/extension_prefs.h

Index: chrome/browser/extensions/extension_prefs.h
diff --git a/chrome/browser/extensions/extension_prefs.h b/chrome/browser/extensions/extension_prefs.h
index 59adfd87de9e0aba24531e4be1d73dcd5e589638..11c7e316bd9bfb12da301e8c96217121b117f0a5 100644
--- a/chrome/browser/extensions/extension_prefs.h
+++ b/chrome/browser/extensions/extension_prefs.h
@@ -56,6 +56,9 @@ class ExtensionPrefs {
   // 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_; }