Set DEVELOPER_DIR in sizes.py on Mac

Otherwise the 'size' command doesn't work unless there's a system xcode around,
which there isn't on newer buildbots.

Bug: 934698
Change-Id: I930ee63b695ab000efa301abc2c169111eb66da3
Reviewed-on: https://chromium-review.googlesource.com/c/1482950
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634643}

infra/scripts/legacy/scripts/slave/chromium/sizes.py

@@ -92,6 +92,12 @@ def main_mac(options, args, results_collector):
   build_dir = build_directory.GetBuildOutputDirectory(SRC_DIR)
   target_dir = os.path.join(build_dir, options.target)
 
+  """Set DEVELOPER_DIR to the hermetic Xcode.app so 'size' will work."""
+  if not 'DEVELOPER_DIR' in os.environ:
+    xcode_path = os.path.join(SRC_DIR, 'build', 'mac_files', 'Xcode.app');
+    if os.path.exists(xcode_path):
+      os.environ['DEVELOPER_DIR'] = xcode_path
+
   result = 0
   # Work with either build type.
   base_names = ('Chromium', 'Google Chrome')