Merge 94986 - Make the ThreadSafeRefCounted support in CrossThreadCopier work for T*.

Merge 94986 - Make the ThreadSafeRefCounted support in CrossThreadCopier work for T*.
https://bugs.webkit.org/show_bug.cgi?id=67947

Reviewed by Adam Barth.

The changes are tested by compiling and added compile asserts to do some verification as well.

* platform/CrossThreadCopier.cpp:
Added some compile asserts to verify various match and non-matches for CrossThreadCopier.
* platform/CrossThreadCopier.h:
Added a typedef to convert T* to T, just like the typedef's to remove RefPtr and PassRefPtr.
Added a compile assert to verify that only one of the typedefs did anything.
(CrossThreadCopierBase<false, true, T>::copy): Remove "get" as it is unnecessary.
It shouldn't have been here (PassRefPtr and RefPtr easily and sometimes more efficiently
convert to PassRefPtr without get). Also, a raw pointer doesn't have a get() method.

TBR=levin@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=96062