mac: Disable clang plugin in asan builds.

asan's clang is currently pinned to a very old revision and hence includes
a very old plugin. Since all other bots run the plugin, we don't really
lose coverage by disabling the plugin on asan bots for now.

BUG=170629
TBR=glider

Review URL: https://chromiumcodereview.appspot.com/14305005

git-svn-id: http://src.chromium.org/svn/trunk/src/build@195479 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -3595,7 +3595,10 @@
                 '$(inherited)', '-std=gnu++11',
               ],
             }],
-            ['clang==1 and clang_use_chrome_plugins==1', {
+            # TODO(thakis): Reenable plugins with once
+            # tools/clang/scripts/update.sh no longer pins clang to an ancient
+            # version for asan (http://crbug.com/170629)
+            ['clang==1 and clang_use_chrome_plugins==1 and asan!=1', {
               'OTHER_CFLAGS': [
                 '<@(clang_chrome_plugins_flags)',
               ],