Allow relative paths to external extension files for some providers, error out for others.

chrome/browser/extensions/external_extension_loader.cc

 // Copyright (c) 2011 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/browser/extensions/external_extension_loader.h"
 
 #include "base/logging.h"
 #include "base/values.h"
 #include "chrome/browser/browser_thread.h"
 #include "chrome/browser/extensions/external_extension_provider_impl.h"
 
 void ExternalExtensionLoader::Init(
     ExternalExtensionProviderImpl* owner) {
   CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   owner_ = owner;
 }
 
+const FilePath ExternalExtensionLoader::GetBaseCrxFilePath() {
+  CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  // By default, relative paths are not supported.
+  // Subclasses that wish to support them should override this method.
+  return FilePath();
+}
+
 void ExternalExtensionLoader::OwnerShutdown() {
   CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   owner_ = NULL;
 }
 
 void ExternalExtensionLoader::LoadFinished() {
   CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   running_ = false;
   if (owner_) {
     owner_->SetPrefs(prefs_.release());
   }
 }