Removing DCHECKs for the dummy plugin parent window which is used as the container window for windowless NPAPI plugins like
flash.

These DCHECKs were in place for checking if the plugin parent window was created successfully. However they fire for Windows 8
ASH because the parent of this window is the windows 8 metro window which cannot be used as the parent outside the metro
process.

Replaced this with checks for ::IsWindow

BUG=301548
TBR=jam

Review URL: https://codereview.chromium.org/75683006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235894 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235894
Revert 235861 "Add ash-enable-immersive-all-windows command line..."

> Add ash-enable-immersive-all-windows command line flag to enable immersive fullscreen for non-frameless v2 apps. (The goal is to add support for immersive fullscreen for v1 apps and miscellaneous windows such as the task manager shortly) When the flag is set, <F4> will put the app into immersive fullscreen.
> 
> In immersive fullscreen, the window header (the title bar and window controls) slide out as an overlay over the web contents when the mouse is hovered at the top of the display.
> 
> chrome.app.window.current().isFullscreen() returns false for immersive fullscreen windows
> Entering fullscreen via the app.window api or webkitRequestFullScreen() quits immersive fullscreen.
> 
> BUG=307622
> R=oshima,benwells
> TBR=sky (For adding VIEWS_EXPORT to ui/views/widget/widget_observer.h)
> TEST=Manual, see steps below:
> 1) Install: https://chrome.google.com/webstore/detail/window-state-sample/hcbhfbnaaancmblfhdknlnojpafjohbi
> 2) Enable "Enable immersive fullscreen for non browser windows" in chrome://flags
> 3) Hit <F4>
> 4) Ensure that the "isFullscreen" checkbox in the app is checked
> 5) Ensure that the shelf light bar is visible (The shelf is not completely hidden)
> 6) Hover the mouse at the top of the screen. Ensure that the window header (maximize and close button slide down and overlay the web contents)
> 7) Move the mouse off of the header. Ensure that the window header slides off screen
> 8) Press the Fullscreen button in the app (It may be useful to set the "chrome.app.window actions delay" to zero seconds)
> 9) Ensure that the shelf is completely hidden.
> 10) Hover the mouse at the top of the screen. Ensure that the header slides out again.
> 11) Press <F4>
> 12) Ensure that the "isFullscreen" checkbox is unchecked
> 13) Ensure that the window header is visible and does not slide out
> 
> Review URL: https://codereview.chromium.org/59043013

BUG=307622,320938
TBR=pkotwicz@chromium.org

Review URL: https://codereview.chromium.org/73623008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235895 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235895