IntersectionObserver: remove gc-timing-revealing execeptions.

IntersectionObserver: remove gc-timing-revealing execeptions.

This also simplifies some of the teardown logic, and eliminates a few
calls to rootIsValid.

BUG=680806
R=esprehn@chromium.org,ojan@chromium.org

Review-Url: https://codereview.chromium.org/2646633002
Cr-Commit-Position: refs/heads/master@{#444566}
Committed: https://chromium.googlesource.com/chromium/src/+/86f8eec3ff39b659e93a70f50aa8e8196277e8a9

[esprehn, 2017-01-18 23:06:25]

lgtm

[szager1, 2017-01-18 23:10:02]

A note about a subtle behavioral change: prior to this CL, if an observer's root
element was gc-ed, then observer.takeRecords() would fail to return any pending
notifications.  With this change, the pending notifications will be delivered.

It's hard to imagine how the old behavior could have been abused.  If a root
element was gc-ed, then the observer would never generate any new notifications,
so you would expect takeRecords() to always come back empty.  Still, out of an
abundance of caution, this change makes takeRecords() follow the same code path
either way.

[szager1, 2017-01-18 23:12:45]

The CQ bit was checked by szager@chromium.org

[commit-bot: I haz the power, 2017-01-18 23:13:17]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-19 00:32:27]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1484781165332840, "parent_rev":
"57fa7c2cd73975510b7018f8470a67bad5f2e544", "commit_rev":
"86f8eec3ff39b659e93a70f50aa8e8196277e8a9"}

[commit-bot: I haz the power, 2017-01-19 00:35:28]

Description was changed from

==========
IntersectionObserver: remove gc-timing-revealing execeptions.

This also simplifies some of the teardown logic, and eliminates a few
calls to rootIsValid.

BUG=680806
R=esprehn@chromium.org,ojan@chromium.org
==========

to

==========
IntersectionObserver: remove gc-timing-revealing execeptions.

This also simplifies some of the teardown logic, and eliminates a few
calls to rootIsValid.

BUG=680806
R=esprehn@chromium.org,ojan@chromium.org

Review-Url: https://codereview.chromium.org/2646633002
Cr-Commit-Position: refs/heads/master@{#444566}
Committed:
https://chromium.googlesource.com/chromium/src/+/86f8eec3ff39b659e93a70f50aa8...
==========

[commit-bot: I haz the power, 2017-01-19 00:35:29]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/86f8eec3ff39b659e93a70f50aa8...