Create AndroidCommandLineBackend to handle setting up cmdline args

tools/telemetry/telemetry/core/backends/android_app_backend.py

Index: tools/telemetry/telemetry/core/backends/android_app_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/android_app_backend.py b/tools/telemetry/telemetry/core/backends/android_app_backend.py
index 196d855d75de903f650fcaac64fbc9b41723eb67..ecb5c6ce00f067deb5513b878266285adbe9033b 100644
--- a/tools/telemetry/telemetry/core/backends/android_app_backend.py
+++ b/tools/telemetry/telemetry/core/backends/android_app_backend.py
@@ -10,9 +10,12 @@ from telemetry.core import util
 from telemetry.core import web_contents
 from telemetry.core.backends import adb_commands
 from telemetry.core.backends import app_backend
+from telemetry.core.backends import android_browser_backend_settings
+from telemetry.core.backends import android_command_line_backend
 
 
 class AndroidAppBackend(app_backend.AppBackend):
+
   def __init__(self, android_platform_backend, start_intent,
                is_app_ready_predicate=None):
     super(AndroidAppBackend, self).__init__(
@@ -23,6 +26,13 @@ class AndroidAppBackend(app_backend.AppBackend):
     self._is_running = False
     self._existing_processes_by_pid = {}
 
+    webview_startup_args = self.GetWebviewStartupArgs()

[nednguyen, 2015/01/13 16:03:04]

Calling a method in the constructor can be dangerous sometimes. How about make
GetWebviewStartupArgs() a classmethod?

[ariblue, 2015/01/13 20:23:37]

I've moved it to the __enter__ function in part of the switch to the
__enter__/__exit__ paradigm.

+    backend_settings = android_browser_backend_settings.WebviewBackendSettings(
+        'android-webview')
+    self._android_command_line_backend = (
+        android_command_line_backend.AndroidCommandLineBackend(
+            self._adb, backend_settings, webview_startup_args))
+
   @property
   def _adb(self):
     return self.platform_backend.adb
@@ -36,10 +46,16 @@ class AndroidAppBackend(app_backend.AppBackend):
     AppStory derivations can customize the wait-for-ready-state to wait
     for a more specific event if needed.
     """
+    self._android_command_line_backend.SetUpCommandLine()

[nednguyen, 2015/01/13 16:03:04]

Instead of try & finally as below, can we use the __enter__ & __exit__ paradigm?

If self._adb.device().StartActivity(self._start_intent, blocking=False) crashes
for example, the cleanup will fail. The "with" paradigm is a pretty nice way to
guarantee the resource cleanup.

[ariblue, 2015/01/13 20:23:37]

Yeah, that looks cleaner too. Good call, updated here and in
android_browser_backend

+
     # TODO(slamm): check if can use "blocking=True" instead of needing to sleep.
     # If "blocking=True" does not work, switch sleep to "ps" check.
     self._adb.device().StartActivity(self._start_intent, blocking=False)
-    util.WaitFor(self._IsAppReady, timeout=60)
+
+    try:
+      util.WaitFor(self._IsAppReady, timeout=60)
+    finally:
+      self._android_command_line_backend.RestoreCommandLine()
     self._is_running = True
 
   def Close(self):
@@ -81,3 +97,15 @@ class AndroidAppBackend(app_backend.AppBackend):
     for process in self.GetProcesses():
       webviews.update(process.GetWebViews())
     return webviews
+
+  def GetWebviewStartupArgs(self):
+    args = []
+
+    # Turn on GPU benchmarking extension for all runs. The only side effect of
+    # the extension being on is that render stats are tracked. This is believed
+    # to be effectively free. And, by doing so here, it avoids us having to
+    # programmatically inspect a pageset's actions in order to determine if it
+    # might eventually scroll.
+    args.append('--enable-gpu-benchmarking')
+
+    return args