MB: Enable optimize_for_fuzzing=true for libfuzzer builds.

tools-webrtc/mb/mb_config.pyl

Index: tools-webrtc/mb/mb_config.pyl
diff --git a/tools-webrtc/mb/mb_config.pyl b/tools-webrtc/mb/mb_config.pyl
index 1a310dd566944d231ed45d734f459fe612f4ec1e..966cc232bb71bc503ed572e33ae886b631448f6e 100644
--- a/tools-webrtc/mb/mb_config.pyl
+++ b/tools-webrtc/mb/mb_config.pyl
@@ -237,7 +237,7 @@
       'gn', 'openh264', 'release', 'static', 'goma', 'x64'
     ],
     'libfuzzer_asan_release_bot_x64': [
-      'libfuzzer', 'asan', 'openh264_release_bot', 'x64'
+      'libfuzzer', 'asan', 'optimize_for_fuzzing', 'openh264_release_bot', 'x64'
     ],
     'memcheck_release_bot_x64': [
       'memcheck', 'gn', 'openh264_release_bot', 'x64'
@@ -416,6 +416,10 @@
       'mixins': ['openh264', 'release_bot'],
     },
 
+    'optimize_for_fuzzing': {
+      'gn_args': 'optimize_for_fuzzing=true',
+    },
+
     'release': {
       'gn_args': 'is_debug=false',
     },