Work on GN build of Chrome.

Fixes the rest of the non-rtc and non-vpx linker errors for the chrome target.

BUG=
[email protected]

Review URL: https://codereview.chromium.org/505853003

Cr-Commit-Position: refs/heads/master@{#291952}
diff --git a/components/copresence.gypi b/components/copresence.gypi
index 6a27d76..6ecd700 100644
--- a/components/copresence.gypi
+++ b/components/copresence.gypi
@@ -19,6 +19,7 @@
         '..',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'copresence/copresence_constants.cc',
         'copresence/copresence_manager.cc',
         'copresence/copresence_manager_impl.cc',