Instrument pepper plugin load failures.

ChromeOS experiences an increased failure to load Pepper Flash plugins.
To help investigate these failures in the field increase logging.
Also disallow npapi plugin generation on ChromeOS as a fallback. We
don't need a zombie process when this failure happens.

BUG=chromium:314301
TEST=kill -stop, reload, kill -9 ppapi process on Pixel.

Review URL: https://codereview.chromium.org/103623003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239740 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239740
Suppress leaks in ExternalMountPoints::RegisterFileSystem

BUG=327280
R=tzik@chromium.org

Review URL: https://codereview.chromium.org/110063003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239741 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239741