Dialogs don't drop tab fullscreen when in FullscreenWithinTab mode.

Overrides the default behavior of dropping fullscreen when a tab modal
dialog is opened in the FullscreenWithinTab case. This is because, in
FWT mode, the browser window is in its normal layout (not fullscreened).

Bug: 883535,812769
Change-Id: I1c262954b962d508eb86ef9a8a312bec03ab2332
Reviewed-on: https://chromium-review.googlesource.com/1228976
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#592522}(cherry picked from commit 1c8c2146c2f99fb7eefb79b170e60f53700f7ab8)
Reviewed-on: https://chromium-review.googlesource.com/1239346
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#565}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}
3 files changed