DevTools: [Console] fix console stick-to-bottom behavior in case of multiline messages

DevTools: [Console] fix console stick-to-bottom behavior in case of multiline messages

The patch fixes the stick-to-bottom behavior of console in case of multiline
messages.

The patch does two things:
1. ViewportControl starts to cache provider's itemCount in invalidate call.
   This ensures that the regular scrolling of viewport is not affected
   by provider's item changes unless an invalidate method was called.

2. Stick to bottom only in case of non-user-generated gestures. This is
   done via transitioning to the event.isTrusted flag.

BUG=594339
R=dgozman, pfeldman

Review URL: https://codereview.chromium.org/1863313002

Cr-Commit-Position: refs/heads/master@{#385872}
(cherry picked from commit 1d413c3ebced31d7182b31ff6efb458c5a12216e)

Committed: https://chromium.googlesource.com/chromium/src/+/7c8faba3e1586366ae97bba310f0aa6df9b14281

[lushnikov, 2016-04-09 00:11:50]

Description was changed from

==========
DevTools: [Console] fix console stick-to-bottom behavior in case of multiline
messages

The patch fixes the stick-to-bottom behavior of console in case of multiline
messages.

The patch does two things:
1. ViewportControl starts to cache provider's itemCount in invalidate call.
   This ensures that the regular scrolling of viewport is not affected
   by provider's item changes unless an invalidate method was called.

2. Stick to bottom only in case of non-user-generated gestures. This is
   done via transitioning to the event.isTrusted flag.

BUG=594339
R=dgozman, pfeldman

Review URL: https://codereview.chromium.org/1863313002

Cr-Commit-Position: refs/heads/master@{#385872}
(cherry picked from commit 1d413c3ebced31d7182b31ff6efb458c5a12216e)
==========

to

==========
DevTools: [Console] fix console stick-to-bottom behavior in case of multiline
messages

The patch fixes the stick-to-bottom behavior of console in case of multiline
messages.

The patch does two things:
1. ViewportControl starts to cache provider's itemCount in invalidate call.
   This ensures that the regular scrolling of viewport is not affected
   by provider's item changes unless an invalidate method was called.

2. Stick to bottom only in case of non-user-generated gestures. This is
   done via transitioning to the event.isTrusted flag.

BUG=594339
R=dgozman, pfeldman

Review URL: https://codereview.chromium.org/1863313002

Cr-Commit-Position: refs/heads/master@{#385872}
(cherry picked from commit 1d413c3ebced31d7182b31ff6efb458c5a12216e)

Committed:
https://chromium.googlesource.com/chromium/src/+/7c8faba3e1586366ae97bba310f0...
==========

[lushnikov, 2016-04-09 00:11:52]

Committed patchset #1 (id:1) manually as
7c8faba3e1586366ae97bba310f0aa6df9b14281.