[ChromeDriver] Support mobile emulation on desktop Chrome.

chrome/test/chromedriver/client/chromedriver.py

Index: chrome/test/chromedriver/client/chromedriver.py
diff --git a/chrome/test/chromedriver/client/chromedriver.py b/chrome/test/chromedriver/client/chromedriver.py
index 946f85cbaf883f8455d7adee17b03da10ad3824a..a646a17441f75be782751c930ab352da5ffd0fab 100644
--- a/chrome/test/chromedriver/client/chromedriver.py
+++ b/chrome/test/chromedriver/client/chromedriver.py
@@ -65,7 +65,7 @@ class ChromeDriver(object):
                android_use_running_app=None, chrome_switches=None,
                chrome_extensions=None, chrome_log_path=None,
                debugger_address=None, browser_log_level=None,
-               experimental_options=None):
+               device_metrics=None, experimental_options=None):
     self._executor = command_executor.CommandExecutor(server_url)
 
     options = {}
@@ -89,6 +89,10 @@ class ChromeDriver(object):
       assert type(chrome_switches) is list
       options['args'] = chrome_switches
 
+    if device_metrics:
+      assert type(device_metrics) is dict
+      options['deviceMetrics'] = device_metrics
+
     if chrome_extensions:
       assert type(chrome_extensions) is list
       options['extensions'] = chrome_extensions