Revert of Fix crash when the source browser window is deleted during a drag (patchset...

Revert of Fix crash when the source browser window is deleted during a drag (patchset #3 id:160001 of https://codereview.chromium.org/795303002/)

Reason for revert:
Since landing this, Linux ChromiumOS Ozone Tests (1) is failing three DND tests.

http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Ozone%20Tests%20%281%29/builds/7685/steps/interactive_ui_tests/logs/stdio

@@@STEP_LOG_LINE@DND@BookmarkBarViewTest5.DND (run #1):@@@
@@@STEP_LOG_LINE@DND@[ RUN      ] BookmarkBarViewTest5.DND@@@
@@@STEP_LOG_LINE@DND@@@@
@@@STEP_LOG_LINE@DND@BookmarkBarViewTest5.DND (run #2):@@@
@@@STEP_LOG_LINE@DND@[ RUN      ] BookmarkBarViewTest5.DND@@@
@@@STEP_LOG_LINE@DND@@@@
@@@STEP_LOG_LINE@DND@BookmarkBarViewTest5.DND (run #3):@@@
@@@STEP_LOG_LINE@DND@[ RUN      ] BookmarkBarViewTest5.DND@@@
@@@STEP_LOG_LINE@DND@@@@
@@@STEP_LOG_LINE@DND@BookmarkBarViewTest5.DND (run #4):@@@
@@@STEP_LOG_LINE@DND@[ RUN      ] BookmarkBarViewTest5.DND@@@
@@@STEP_LOG_LINE@DND@@@@
@@@STEP_LOG_END@DND@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@BookmarkBarViewTest7.DNDToDifferentMenu (run #1):@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@[ RUN      ] BookmarkBarViewTest7.DNDToDifferentMenu@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@BookmarkBarViewTest7.DNDToDifferentMenu (run #2):@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@[ RUN      ] BookmarkBarViewTest7.DNDToDifferentMenu@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@BookmarkBarViewTest7.DNDToDifferentMenu (run #3):@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@[ RUN      ] BookmarkBarViewTest7.DNDToDifferentMenu@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@BookmarkBarViewTest7.DNDToDifferentMenu (run #4):@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@[ RUN      ] BookmarkBarViewTest7.DNDToDifferentMenu@@@
@@@STEP_LOG_LINE@DNDToDifferentMenu@@@@
@@@STEP_LOG_END@DNDToDifferentMenu@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@BookmarkBarViewTest8.DNDBackToOriginatingMenu (run #1):@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@[ RUN      ] BookmarkBarViewTest8.DNDBackToOriginatingMenu@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@BookmarkBarViewTest8.DNDBackToOriginatingMenu (run #2):@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@[ RUN      ] BookmarkBarViewTest8.DNDBackToOriginatingMenu@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@BookmarkBarViewTest8.DNDBackToOriginatingMenu (run #3):@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@[ RUN      ] BookmarkBarViewTest8.DNDBackToOriginatingMenu@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@BookmarkBarViewTest8.DNDBackToOriginatingMenu (run #4):@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@[ RUN      ] BookmarkBarViewTest8.DNDBackToOriginatingMenu@@@
@@@STEP_LOG_LINE@DNDBackToOriginatingMenu@@@@
@@@STEP_LOG_END@DNDBackToOriginatingMenu@@@

Original issue's description:
> Fix crash when the source browser window is deleted during a drag
>
> This CL makes Widget::RunShellDrag() and DesktopDragDropClientWin not crash if
> the browser window is deleted during a drag-drop operation. An extension can
> delete the browser window during the drag-drop operation.
>
> BUG=440534
> TEST=BookmarkBarViewTest22.*
>
> Committed: https://crrev.com/460bdd69c6f96191a4293da61e9e4999acd0f5ff
> Cr-Commit-Position: refs/heads/master@{#309360}

TBR=sky@chromium.org,pkotwicz@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=440534

Review URL: https://codereview.chromium.org/818983002

Cr-Commit-Position: refs/heads/master@{#309367}