DevTools: [Console] fix certain case that forces console to shake

DevTools: [Console] fix certain case that forces console to shake

Currently, ViewportControl uses clientHeight of its main element to
estimate visible viewport height. This falls shortly under the following
scenario:
1. ViewportControl has its "stickToBottom" flag set to true and just
scrolled to bottom as its "refresh" method got executed. Note, that
this refresh has scheduled one more scroll as it "scrolls to bottom".
2. The "refresh" method call figured out that there's a necessity to
render one more element in the beginning of viewport, and this new
element happen to add a horizontal scroll to the console.
3. Another "refresh" method gets executed (it was scheduled in #1)
4. The method figures out that client height changed (due to added
horizontal scroller), thus first element not needed any more and
gets removed from viewport.
5. Goto #1.

This change migrates from using clientHeight to using offsetHeight
which doesn't change as horizontal scroller gets added or removed in
result of viewport rendering.

BUG=387465
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178422

[lushnikov, 2014-07-17 12:01:31]

ptal

[aandrey, 2014-07-17 12:09:46]

looks good.
will it be easy to add a test for this?

[lushnikov, 2014-07-17 12:36:44]

The preconditions for this situation are fragile and hardly reproducible - its a
matter of a couple of pixels and
depends on such things like scrollbar height. And given the history of
crbug.com/390204, it will take a lot of effort to make it
stable on all platforms. I believe it doesn't worth it.

[pfeldman, 2014-07-17 17:41:08]

lgtm

[lushnikov, 2014-07-17 17:41:16]

The CQ bit was checked by lushnikov@chromium.org

[commit-bot: I haz the power, 2014-07-17 17:42:10]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/lushnikov@chromium.org/396853005/1

[commit-bot: I haz the power, 2014-07-17 19:00:37]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/17537)
  mac_gpu_retina_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu_retina_tr...)

[commit-bot: I haz the power, 2014-07-17 19:22:59]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-07-17 19:23:00]

Try jobs failed on following builders:
  mac_gpu_retina_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu_retina_tr...)

[lushnikov, 2014-07-18 08:44:57]

The CQ bit was checked by lushnikov@chromium.org

[commit-bot: I haz the power, 2014-07-18 08:45:23]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/lushnikov@chromium.org/396853005/1

[commit-bot: I haz the power, 2014-07-18 08:45:56]

Change committed as 178422