clang: Disable new warning -Wbitfield-width on the ToT bots.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index f7d2141a4ce7e02e8679e27e8d227cab6aad1294..1c1c731b7d9fc6bea81ac0bd8778f73ea1a5b55e 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -3108,6 +3108,12 @@
         # TODO: Enable on Windows too, http://crbug.com/404525
         'variables': { 'clang_warning_flags': ['-Wexit-time-destructors']},
       }],
+      ['"<!(python <(DEPTH)/tools/clang/scripts/update.py --print-revision)"!="245965-1"', {
+        # TODO(thakis): Move this to the global clang_warning_flags block once
+        # clang is rolled far enough that the pinned clang understands this flag
+        # TODO(thakis): Consider enabling this?
+        'variables': { 'clang_warning_flags': ['-Wno-bitfield-width']},
+      }],
       ['chromium_code==0', {
         'variables': {
           'clang_warning_flags': [