[DevTools] Do not access WebViewImpl and WebDevToolsAgentClient when closing.

BUG=312393, 344623
R=dgozman@chromium.org, yurys@chromium.org

Review URL: https://codereview.chromium.org/172463002

git-svn-id: svn://svn.chromium.org/blink/trunk@167585 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert 167543 "Don't ignore size updates that have a width and h..."

The CL broke webkit_unit_tests in Android builds:
http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/18729/steps/webkit_unit_tests/logs/stdio#failure1

> Don't ignore size updates that have a width and height == 0.
> 
> It is perfectly legal for the Android WebView to have a zero height,
> this is frequenly how a new WebView is first laid out. Rejecting the
> initial (width, 0) size update causes the initial layout to be
> too narrow.
> 
> BUG=344885
> 
> Review URL: https://codereview.chromium.org/172203003

TBR=mkosiba@chromium.org

Review URL: https://codereview.chromium.org/165993009

git-svn-id: svn://svn.chromium.org/blink/trunk@167586 bbb929c8-8fbe-4397-9dbb-9b2b20218538