Cherry pick   Android WebView: clean up the AwContentsClientBridge webcontents userdata.

Bug: 17396873

Original description:

When we destroy the AwContentsClientBridge, clear the pointer to it
held by webcontents user data.

Also ensure that if we don't post the callback to the java side
to run the js dialog callback in the embedding app that we run
the callback.

BUG=411399
Committed: https://chromium.googlesource.com/chromium/src/+/bafb7ef3239ed1db29393ca1d528af08a2f19dfb

Change-Id: Ib9fbb4fc6b4e4dc45688db814e3ec886d469e222
5 files changed