
Return value of goog.events and goog.events.listenOnce is going to
change from ?number to goog.events.ListenableKey. As a first step, we
are switching the return value to a typedef goog.events.Key (currently
just typedef to ?number). This CL switches JS files to use this typedef.

Obviously, the subsequent change will be problematic if this code
make an assumption that the return value is a number and uses the return
value in context where the number is required (e.g. goog.isNumber, using
it as index to an array). While I've tried my best to fix these usages,
I may have missed some of them. Please check that the code will still
remain correct if the return value of goog.events.listen/listenOnce is
changed to an object (goog.events.ListenableKey). Furthermore, if
you know of any other location where the return value is used in a context
that require it to be numbers, please send me a quick email.

This is parts of goog.events refactoring to remove leaking listeners
problem.

Tested:
TAP presubmits for global presubmit queue
http://test/OCL:41250199:BASE:41269811:1358405130847:6908b354
Some tests failed; test failures are believed to be unrelated to this CL

R=cibu
DELTA=6 (0 added, 0 deleted, 6 changed)


Revision created by MOE tool push_codebase.
MOE_MIGRATION=6162


git-svn-id: 35241bd708fe29f1f6c7a4322d322e99ff93b95e@2448 0b95b8e8-c90f-11de-9d4f-f947ee5921c8

weitzj/closure-library,weitzj/closure-library