Add unit test for the Settings API Bubble.

extensions/browser/extension_prefs.cc

 // 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.
 
 #include "extensions/browser/extension_prefs.h"
 
 #include <iterator>
 
 #include "base/command_line.h"
 #include "base/prefs/pref_notifier.h"
@@ skipping 1842 matching lines @@
     DVLOG(1) << "SetInstallSignature - saving";
   } else {
     DVLOG(1) << "SetInstallSignature - clearing";
     prefs_->ClearPref(kInstallSignature);
   }
 }
 
 std::string ExtensionPrefs::GetInstallParam(
     const std::string& extension_id) const {
   const base::DictionaryValue* extension = GetExtensionPref(extension_id);
-  if (!extension) {
-    NOTREACHED();
+  if (!extension)  // Expected during unit testing.
     return std::string();
-  }
   std::string install_parameter;
   if (!extension->GetString(kPrefInstallParam, &install_parameter))
     return std::string();
   return install_parameter;
 }
 
 void ExtensionPrefs::SetInstallParam(const std::string& extension_id,
                                      const std::string& install_parameter) {
   UpdateExtensionPref(extension_id,
                       kPrefInstallParam,
@@ skipping 280 matching lines @@
   extension_pref_value_map_->RegisterExtension(
       extension_id, install_time, is_enabled, is_incognito_enabled);
 
   FOR_EACH_OBSERVER(
       ExtensionPrefsObserver,
       observer_list_,
       OnExtensionRegistered(extension_id, install_time, is_enabled));
 }
 
 }  // namespace extensions