[Telemetry]: Add --target-arch option to browser options.

tools/telemetry/telemetry/core/browser_options.py

Index: tools/telemetry/telemetry/core/browser_options.py
diff --git a/tools/telemetry/telemetry/core/browser_options.py b/tools/telemetry/telemetry/core/browser_options.py
index 058c62ea810d818cbd308828845af98d3c133a87..0297ab00494232d64e245791a82e1c37c193248e 100644
--- a/tools/telemetry/telemetry/core/browser_options.py
+++ b/tools/telemetry/telemetry/core/browser_options.py
@@ -76,6 +76,11 @@ class BrowserFinderOptions(optparse.Values):
         dest='android_device',
         help='The android device ID to use'
              'If not specified, only 0 or 1 connected devcies are supported.')
+    group.add_option('--target-arch',
+        dest='target_arch',
+        help='The target architecture of the browser. Options available are: '
+             'x64, x86_64, arm, arm64 and mips. '
+             'Defaults to the default architecture of the platform if omitted.')
     group.add_option(
         '--remote',
         dest='cros_remote',