Add support for command line switches to Features, and as proof that it works,

chrome/common/extensions/manifest_tests/extension_manifests_platformapp_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 "base/command_line.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/memory/linked_ptr.h"
 #include "chrome/common/extensions/manifest_handlers/app_isolation_info.h"
 #include "chrome/common/extensions/manifest_tests/chrome_manifest_test.h"
 #include "extensions/common/error_utils.h"
@@ skipping 111 matching lines @@
     const char* api_name = kPlatformAppExperimentalApis[i];
 
     // DictionaryValue will take ownership of this ListValue.
     base::ListValue *permissions = new base::ListValue();
     permissions->Append(new base::StringValue("experimental"));
     permissions->Append(new base::StringValue(api_name));
     manifest->Set("permissions", permissions);
     manifests.push_back(make_linked_ptr(manifest->DeepCopy()));
   }
 
-  // First try to load without any flags. This should fail for every API.
+  // First try to load without any flags. This should warn for every API.
   for (size_t i = 0; i < arraysize(kPlatformAppExperimentalApis); ++i) {
-    LoadAndExpectError(ManifestData(manifests[i].get(), ""),
-                       errors::kExperimentalFlagRequired);
+    LoadAndExpectWarning(
+        ManifestData(manifests[i].get(), ""),
+        "'experimental' requires the 'experimental-extension-apis' "
+        "command line switch to be enabled.");
   }
 
   // Now try again with the experimental flag set.
   CommandLine::ForCurrentProcess()->AppendSwitch(
       switches::kEnableExperimentalExtensionApis);
   for (size_t i = 0; i < arraysize(kPlatformAppExperimentalApis); ++i) {
     LoadAndExpectSuccess(ManifestData(manifests[i].get(), ""));
   }
 }
 
 }  // namespace extensions