Compute a length based on heap size instead of card table size.

The card from address computation checks that the argument is a valid
card.  However, the limit points just past the end of the last card so
it is often invalid.  This fixes a crash in asserts-enabled builds.

Change-Id: I5d7f0a4753703f82b2e1be520e6108d1b61b22d3
1 file changed