Add -fvisibility=default to metrics library

BUG=chromium:315243
TEST=x86-generic-full and daisy-full trybots pass

Change-Id: Ia1f2d41ddf0e54beee0a928bc62b67edd71ac706
Reviewed-on: https://chromium-review.googlesource.com/175770
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Liam McLoughlin <lmcloughlin@chromium.org>
Tested-by: Liam McLoughlin <lmcloughlin@chromium.org>
diff --git a/metrics/metrics.gyp b/metrics/metrics.gyp
index 67e7c37..9709c35 100644
--- a/metrics/metrics.gyp
+++ b/metrics/metrics.gyp
@@ -30,6 +30,9 @@
     {
       'target_name': 'libmetrics',
       'type': 'shared_library',
+      'cflags': [
+        '-fvisibility=default',
+      ],
       'sources': [
         'c_metrics_library.cc',
         'metrics_library.cc',