Add a new field "source" in launchData of chrome.app.runtime.onLaunched() to trace launch source.

extensions/common/switches.cc

 // Copyright 2013 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/common/switches.h"
 
 namespace extensions {
 
 namespace switches {
 
@@ skipping 81 matching lines @@
 // as --scripts-require-action=1.
 const char kEnableScriptsRequireAction[] = "enable-scripts-require-action";
 
 // Makes component extensions appear in chrome://settings/extensions.
 const char kShowComponentExtensionOptions[] =
     "show-component-extension-options";
 
 // Adds the given extension ID to all the permission whitelists.
 const char kWhitelistedExtensionID[] = "whitelisted-extension-id";
 
+// Pass launch source to platform apps.
+const char kTraceAppSource[] = "enable-trace-app-source";
+
 }  // namespace switches
 
 }  // namespace extensions