aura: Ensure OwnedMailbox not used with invalid or destroyed GLHelper.

There are 2 scenarios when the GLHelper becomes invalid:

1. On lost context. In this case, the OwnedMailbox is reset and the
pointer is destroyed. However, the copy request result code would
continue trying to use the OwnedMailbox regardless. Instead we can
use this as a hint that the mailbox is no longer valid and abort the
readback.

2. On shutdown. Once the RenderWidgetHostViewAura is shutdown, there
is no way to easily tell if the GLHelper attached to the OwnedMailbox
being stored in copy request callbacks is still alive. Since a readback
on the RenderWidgetHostViewAura can not complete once the RWHVA class
is destroyed anyways, we can destroy the contents of the OwnedMailboxes
in flight at that time. This way when the readback is later aborted,
the OwnedMailbox does not try to clean itself up with a potentially
destroyed GLHelper.

R=piman@chromium.org
BUG=270918

Review URL: https://codereview.chromium.org/120913004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243971 0039d316-1c4b-4281-b951-d872f2087c98
Make V8ValueConverterImpl serialize objects with internal field counts to an
empty object rather than skipping them altogether. This is more consistent with
the expected behaviour of extension APIs.

BUG=330559
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/129153002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243972 0039d316-1c4b-4281-b951-d872f2087c98
[Telemetry]: Fix v8_object_stats metric to avoid having a '.' in trace names

Review URL: https://codereview.chromium.org/132213002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243973 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243972
SVN changes up to revision 243973