Add a --startup option to generate combined traces for startup.

tools/profile_chrome/chrome_startup_controller_unittest.py

+# Copyright 2015 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.
+
+import os
+import json
+
+from profile_chrome import chrome_startup_controller
+from profile_chrome import controllers_unittest
+
+
+class ChromeControllerTest(controllers_unittest.BaseControllerTest):
+  def testTracing(self):
+    controller = chrome_startup_controller.ChromeStartupTracingController(
+        self.device, self.package_info, False, 'https://www.google.com')
+
+    interval = 1
+    try:
+      controller.StartTracing(interval)
+    finally:
+      controller.StopTracing()
+
+    result = controller.PullTrace()
+    try:
+      with open(result) as f:
+        json.loads(f.read())
+    finally:
+      os.remove(result)