android: Add CHECK() calls to better understand memory corruption.

This patch adds two CHECK() calls for each call to
base::android::AttachCurrentThread() and base::android::DetachFromVM(),
in order to better understand the mysterious crashers described in
http://crbug.com/322200

BUG=322200
R=bulach@chromium.org,torne@chromium.org,joth@chromium.org

Review URL: https://codereview.chromium.org/86013003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237591 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237591