Enable strict virtual annotation checks for Mac.

BUG=417463

Review URL: https://codereview.chromium.org/848973002

Cr-Commit-Position: refs/heads/master@{#311365}

build/common.gypi

@@ -2136,7 +2136,7 @@
         'conditions': [
           # TODO(dcheng): https://crbug.com/417463 -- work to enable this flag
           # on all platforms is currently underway.
-          ['OS=="linux" and chromeos==0', {
+          ['(OS=="linux" and chromeos==0) or OS=="mac"', {
             'clang_chrome_plugins_flags': [
               '-Xclang',
               '-plugin-arg-find-bad-constructs',