Grab document and position locks in the correct order.

This should prevent deadlock.

R=brianwilkerson@google.com
BUG=

Review URL: https://codereview.chromium.org//681493004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41298 260f80e4-7a28-3924-810f-c04153c831b5
DEPS AutoUpdate: webkit to 184390 (2014-10-24 16:13:44 -0700) leafp@google.com
Generate dart:blink from webkit scripts
http://src.chromium.org/viewvc/blink?view=rev&revision=184390

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41299 260f80e4-7a28-3924-810f-c04153c831b5