Change ComponentLoader::AddOrReplace to return an empty string on failure.

chrome/browser/extensions/component_loader_unittest.cc

 // Copyright (c) 2012 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/component_loader.h"
 
 #include <string>
 
 #include "base/file_util.h"
 #include "base/path_service.h"
@@ skipping 274 matching lines @@
   EXPECT_EQ(default_count + 1, extension_service_.extensions()->size());
 }
 
 TEST_F(ComponentLoaderTest, AddOrReplace) {
   EXPECT_EQ(0u, component_loader_.registered_extensions_count());
   component_loader_.AddDefaultComponentExtensions(false);
   size_t const default_count = component_loader_.registered_extensions_count();
   base::FilePath known_extension = GetBasePath()
       .AppendASCII("override_component_extension");
   base::FilePath unknow_extension = extension_path_;
+  base::FilePath invalid_extension = GetBasePath().AppendASCII("bad");
 
   // Replace a default component extension.
   component_loader_.AddOrReplace(known_extension);
   EXPECT_EQ(default_count,
             component_loader_.registered_extensions_count());
 
   // Add a new component extension.
   component_loader_.AddOrReplace(unknow_extension);
   EXPECT_EQ(default_count + 1,
             component_loader_.registered_extensions_count());
 
   extension_service_.set_ready(true);
   component_loader_.LoadAll();
 
   EXPECT_EQ(default_count + 1, extension_service_.extensions()->size());
   EXPECT_EQ(0u, extension_service_.unloaded_count());
 
   // replace loaded component extension.
   component_loader_.AddOrReplace(known_extension);
   EXPECT_EQ(default_count + 1, extension_service_.extensions()->size());
   EXPECT_EQ(1u, extension_service_.unloaded_count());
+
+  // Add an invalid component extension.
+  std::string extension_id = component_loader_.AddOrReplace(invalid_extension);
+  EXPECT_TRUE(extension_id.empty());
 }
 
 }  // namespace extensions