Fix bug in CSSOM window.scroll api

Use inert-visual-viewport flag correctly.

With the inert-visual-viewport flag set, window.scrollBy and window.scrollTo
should only scroll the layout viewport. Found a logic error where we don't
check this flag before calculating current offset.

This CL also updates the visual viewport to only fire scroll event when the
inert-visual-viewport flag is off.

BUG=489206
Committed: https://crrev.com/b4aaa1da24bbd70c05694837a110a45147fa5c16
Cr-Commit-Position: refs/heads/master@{#357887}

[ymalik, 2015-11-04 19:16:14]

Description was changed from

==========
Fix bug in CSSOM window.scroll api

With the inert-visual-viewport flag set, window.scrollBy and window.scrollTo
should only scroll the layout viewport. Found a logic error where we don't
check this flag before calculating current offset.

BUG=489206
==========

to

==========
Use inert-visual-viewport flag correctly.

With the inert-visual-viewport flag set, window.scrollBy and window.scrollTo
should only scroll the layout viewport. Found a logic error where we don't
check this flag before calculating current offset.

This CL also updates the visual viewport to only fire scroll event when the
inert-visual-viewport flag is off.

BUG=489206
==========

[ymalik, 2015-11-04 19:17:01]

ymalik@chromium.org changed reviewers:
+ bokan@chromium.org

[bokan, 2015-11-04 19:30:53]

lgtm

[ymalik, 2015-11-04 20:31:34]

The CQ bit was checked by ymalik@chromium.org

[commit-bot: I haz the power, 2015-11-04 20:32:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1419143007/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1419143007/20001

[commit-bot: I haz the power, 2015-11-04 20:37:59]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-04 20:39:01]

Patchset 2 (id:??) landed as
https://crrev.com/b4aaa1da24bbd70c05694837a110a45147fa5c16
Cr-Commit-Position: refs/heads/master@{#357887}