Add is_chrome_branded to kythe codesearch builds

Bug: b/140589523
Change-Id: I01e015551729dc440187735fd689486eaabd6cf8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1838053Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Anthony Polito <apolito@google.com>
Cr-Commit-Position: refs/heads/master@{#704808}

tools/mb/mb_config.pyl

@@ -2139,11 +2139,15 @@
 
     # Settings used by the codesearch builders to generate cross-references.
     'codesearch': {
-      'gn_args': 'clang_use_chrome_plugins=false enable_kythe_annotations=true',
+      'gn_args': ('clang_use_chrome_plugins=false '
+                  'enable_kythe_annotations=true '
+                  'is_chrome_branded=true'),
       'mixins': ['goma', 'clang', 'shared', 'debug', 'minimal_symbols'],
     },
     'codesearch_release': {
-      'gn_args': 'clang_use_chrome_plugins=false enable_kythe_annotations=true',
+      'gn_args': ('clang_use_chrome_plugins=false '
+                  'enable_kythe_annotations=true '
+                  'is_chrome_branded=true'),
       'mixins': ['release', 'static', 'goma'],
     },