Calls to HCheckFunction can be eliminated if the value is an HConstant

Calls to HCheckFunction can be eliminated if the value is an HConstant 
function, and that function handle matches the target handle.

BUG=
R=danno@chromium.org, mstarzinger@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=15540

[danno, 2013-07-05 12:57:33]

LGTM, but please make sure that all the tests run and that the mozilla tests
run, too. :-)

[Michael Starzinger, 2013-07-05 13:09:06]

Not looking good yet.

https://codereview.chromium.org/18751003/diff/1/src/hydrogen-instructions.cc
File src/hydrogen-instructions.cc (right):

https://codereview.chromium.org/18751003/diff/1/src/hydrogen-instructions.cc#...
src/hydrogen-instructions.cc:1695: HConstant::cast(value())->Hashcode() ==
target_unique_id_.Hashcode())
This might lead to hash collisions for values that are actually not equal.
Better introduce a HConstant::IsUniqueValue(UniqueValueId id) that does a real
comparison of the ids or returns false if the HConstant doesn't have an id.

[mvstanton, 2013-07-08 08:43:05]

Michael, PTAL. Danno, I ran through Mozilla tests as well, successfully with the
formulation of adding JSFunction to the test in PropertyCell::UpdateType()

[Michael Starzinger, 2013-07-08 08:59:39]

LGTM.

[mvstanton, 2013-07-08 09:01:14]

Committed patchset #2 manually as r15540 (presubmit successful).