[Telemetry] Work around mac-builder-perf failures

All builds on MacOS are failing on perf waterfall due to Widevine
signature errors. Adding a quick workaround with gn flag
enable_widevine_cdm_host_verification=false, as suggested by the
error message.

TBR=wenbinzhang@google.com

Bug: 1128811
Change-Id: Iffa58fe5ff0676e185b8cb381268d28482011172
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412934Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807354}

tools/mb/mb_config.pyl

@@ -2162,7 +2162,7 @@
     ],
 
     'official_goma_mac_perf': [
-      'official', 'goma', 'no_keystone_registration_framework', 'full_symbols',
+      'official', 'goma', 'no_keystone_registration_framework', 'no_widevine_cdm_host_verification', 'full_symbols',
     ],
 
     'official_goma_mac_pgo': [
@@ -2897,6 +2897,10 @@
       'gn_args': 'symbol_level=0',
     },
 
+    'no_widevine_cdm_host_verification': {
+      'gn_args': 'enable_widevine_cdm_host_verification=false',
+    },
+
     'official': {
       'mixins': ['official_optimize'],
       'gn_args': 'is_chrome_branded=true',