Revert "Security drop fullscreen for any nested WebContents level."

This reverts commit 3dcaec6e30feebefc11ee6972a76d446257b28a6.

Reason for revert: Failing Linux MSan tests

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20MSan%20Tests/11191

DevTools listening on ws://127.0.0.1:34267/devtools/browser/a12caedc-549b-4d49-b9bb-a0519f91f318
==14126==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x3c2bb23 in ExitFullscreenModeForTab ./../../content/browser/web_contents/web_contents_impl_browsertest.cc:1561:9

Original change's description:
> Security drop fullscreen for any nested WebContents level.
> 
> BUG=873080
> TEST=as in bug
> 
> Change-Id: Icd75715ac42789c84870967b11c9917a972ae086
> Reviewed-on: https://chromium-review.googlesource.com/1173342
> Commit-Queue: Avi Drissman <avi@chromium.org>
> Reviewed-by: Sidney San Martín <sdy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#582970}

TBR=avi@chromium.org,sdy@chromium.org

Change-Id: I52a9b29f2d17ea6e7db0128815653de624fa5b13
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 873080
Reviewed-on: https://chromium-review.googlesource.com/1174640
Reviewed-by: Chris Mumford <cmumford@chromium.org>
Commit-Queue: Chris Mumford <cmumford@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583071}
3 files changed