Make Callback.Equals() only work when comparing against the same type.

Make Callback.Equals() only work when comparing against the same type.

Previously, we were using the base class's comparator to check equality, which allows us to make comparisons across callbacks of different types. This disallows such a thing.

BUG=none
TEST=New no-compile test.

[awong, 2011-09-10 00:37:34]

Okay, this is actually useful.

[willchan no longer on Chromium, 2011-09-10 00:40:59]

http://codereview.chromium.org/7780016/diff/1/base/bind_unittest.nc
File base/bind_unittest.nc (left):

http://codereview.chromium.org/7780016/diff/1/base/bind_unittest.nc#oldcode82
base/bind_unittest.nc:82: 
Why are these getting deleted?

[awong, 2011-09-10 00:57:45]

http://codereview.chromium.org/7780016/diff/1/base/bind_unittest.nc
File base/bind_unittest.nc (left):

http://codereview.chromium.org/7780016/diff/1/base/bind_unittest.nc#oldcode82
base/bind_unittest.nc:82: 
On 2011/09/10 00:40:59, willchan wrote:
> Why are these getting deleted?

I just moved them. They're in callback_unittest.nc....which I apparently forgot
to add. reuploaded.

[willchan no longer on Chromium, 2011-09-10 01:00:34]

LGTM

[awong, 2011-09-10 04:10:48]

On 2011/09/10 01:00:34, willchan wrote:
> LGTM

Committed as http://src.chromium.org/viewvc/chrome?view=rev&revision=100564