GitLab

- Previously, we had an unguarded bool flag for whether an interface lookup had been logged to UMA. Now each InterfaceInfo has a lock+flag. Should be near-zero contention.
- Previously, PpapiGlobals::GetBrowserSender did lazy creation with no synchronization. Now we create it at process startup and clear it at process shutdown, so there should be no race while the plugin is running.

BUG=413513,414150

Committed: https://crrev.com/d1b2c8f719b0ab471a476bf53911a3657bb4c06a
Cr-Commit-Position: refs/heads/master@{#294715}

Review URL: https://codereview.chromium.org/568793002

Cr-Commit-Position: refs/heads/master@{#295551}