Fix potential crash in WebEmbeddedWorkerImpl

Calling Client::workerContextFailedToStart() could immediately delte
WebEmbeddedWorkerImpl, so it shouldn't touch its member variable
after that.

(Without this fix the SW layout test could crash after browser-side
patch lands in chromium)

BUG=285976
TEST=virtual/serviceworker/http/tests/serviceworker/registration.html

Review URL: https://codereview.chromium.org/152883004

git-svn-id: svn://svn.chromium.org/blink/trunk@166731 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert of Use removeFontFace to avoid resetting fontSelector. (https://codereview.chromium.org/82583005/)

Reason for revert:
This CL appears to have broken

org.chromium.android_webview.test.AwSettingsTest#testLayoutAlgorithmWithTwoViews

in androidwebview_instrumentation_tests.

http://build.chromium.org/p/chromium.webkit/builders/Android%20Tests%20%28dbg%29/builds/17264

Original issue's description:
> Use removeFontFace to avoid resetting fontSelector.
> 
> BUG=305885,336756
> TEST=fast/css/font-face-remove.html, fast/css/font-face-html-as-svg.html
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166681

TBR=ksakamoto@chromium.org,esprehn@chromium.org,ojan@chromium.org,dglazkov@chromium.org,tasak@google.com
NOTREECHECKS=true
NOTRY=true
BUG=305885,336756

Review URL: https://codereview.chromium.org/157853002

git-svn-id: svn://svn.chromium.org/blink/trunk@166732 bbb929c8-8fbe-4397-9dbb-9b2b20218538