Fix crash in WebViewImpl::contentsPreferredMinimumSize

Fix crash in WebViewImpl::contentsPreferredMinimumSize

The call to layout() could invalidate some of the null-checks we did previously.
Instead layout first, then do all the null checks.

BUG=521479
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200743

[Rick Byers, 2015-08-17 21:38:33]

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

[Rick Byers, 2015-08-17 21:38:34]

bokan@ PTAL
Sorry I missed this.  There may have been a pre-existing bug here, but I
definitely made it a lot worse / easier to trigger.

[bokan, 2015-08-18 12:37:52]

lgtm

[Rick Byers, 2015-08-18 13:45:46]

The CQ bit was checked by rbyers@chromium.org

[commit-bot: I haz the power, 2015-08-18 13:45:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1291343008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1291343008/1

[commit-bot: I haz the power, 2015-08-18 15:49:54]

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

[commit-bot: I haz the power, 2015-08-18 15:49:55]

Try jobs failed on following builders:
  linux_chromium_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[Rick Byers, 2015-08-18 17:48:07]

The CQ bit was checked by rbyers@chromium.org

[commit-bot: I haz the power, 2015-08-18 17:48:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1291343008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1291343008/1

[commit-bot: I haz the power, 2015-08-18 18:54:45]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200743