Revert 225099 "Cancel resources in the plugin process when a use..."

Revert 225099 "Cancel resources in the plugin process when a use..."

Reason: androidwebview_instrumentation_tests failing starting from this build:
http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/14741

Locally verified that at least this test starts passing after revert:
org.chromium.android_webview.test.AndroidScrollIntegrationTest#testNoSpuriousOverScrolls

Unsolved mystery remains around the passing trybot with the Rietveld issue:
http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered_tests/builds/89522

> Cancel resources in the plugin process when a user presses the stop button or window.stop() is called.
>
> BUG=286074
> R=ananta@chromium.org
>
> Review URL: https://codereview.chromium.org/24302012

TBR=jam@chromium.org

Review URL: https://codereview.chromium.org/24570003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225179 0039d316-1c4b-4281-b951-d872f2087c98