Fix zygote live/mark bitmap size.

Fixed some errors with the sizes of mark/live bitmaps after zygote space creation.

This was causing us to occasionally have overlapping mark/live bitmaps.

Added a new verify objects mode called VERIFY_OBJECT_FAST which only checks objects and not their classes.

Refactored/optimized some of the scanning code to use xor to clear bits instead of and+not.

Change-Id: Iec87d9157f69e6a558e300950b51d8781679e3f7
diff --git a/src/globals.h b/src/globals.h
index 0efa7eb..1eeaca2 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -36,6 +36,7 @@
 const int kBitsPerByte = 8;
 const int kBitsPerByteLog2 = 3;
 const int kBitsPerWord = kWordSize * kBitsPerByte;
+const int kWordHighBitMask = 1 << (kBitsPerWord - 1);
 
 // Required stack alignment
 const int kStackAlignment = 16;