Always specify current OS when syncing Chromium.

Recently, we've hit a rare case of a dependency being
present only below 'unix' and not in the 'android' section
of the DEPS file in Chromium (src/third_party/junit/src).

This exposed a bug in our sync_chromium.py script, which is that
when the --deps flag is passed to gclient sync, _only_ that platform
is processed. That means our Android builders synced with --deps=android
and thus only getting the Android deps, not the 'unix' ones (Linux).
That behavior is different from a regular gclient sync, where both
the current platform's DEPS and the one specified by appending a target_os
variable into .gclient is used.

Ensuring that we pass both the current platform and the optionally specified
DEPS platform into our sync_chromium.py sync, gives us the same behavior
as a regular sync for the special Chromium sync we use.

TESTED=
First:
rm chromium/.last_sync_chromium
Then I ran without this patch and with target_os = ["android"] in .gclient. Verified
that --deps=android was passed.
With this patch, I repeated the above and verified --deps=unix,android was passed.

R=phoglund@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/52379004

Cr-Commit-Position: refs/heads/master@{#9103}

sync_chromium.py

@@ -35,6 +35,20 @@ SCRIPT_VERSION = 4
 ROOT_DIR = os.path.dirname(os.path.abspath(__file__))
 CHROMIUM_NO_HISTORY = 'CHROMIUM_NO_HISTORY'
 
+# Duplicated from depot_tools/gclient.py since we cannot depend on that:
+DEPS_OS_CHOICES = {
+  "win32": "win",
+  "win": "win",
+  "cygwin": "win",
+  "darwin": "mac",
+  "mac": "mac",
+  "unix": "unix",
+  "linux": "unix",
+  "linux2": "unix",
+  "linux3": "unix",
+  "android": "android",
+}
+
 def _parse_gclient_dict():
   gclient_dict = {}
   try:
@@ -51,7 +65,12 @@ def get_cache_dir():
 
 
 def get_target_os_list():
-  return ','.join(_parse_gclient_dict().get('target_os', []))
+  # Always add the currently running OS since the --deps option will override
+  # that if specified:
+  target_os_list = [DEPS_OS_CHOICES.get(sys.platform, 'unix')]
+  # Add any target_os entries from .gclient.
+  target_os_list += _parse_gclient_dict().get('target_os', [])
+  return ','.join(target_os_list)
 
 
 def main():