Remove some asserts to speed up debug mode.

src/incremental-marking-inl.h

Index: src/incremental-marking-inl.h
===================================================================
--- src/incremental-marking-inl.h	(revision 9581)
+++ src/incremental-marking-inl.h	(working copy)
@@ -143,9 +143,6 @@
 
 
 void IncrementalMarking::WhiteToGrey(HeapObject* obj, MarkBit mark_bit) {
-  ASSERT(Marking::MarkBitFrom(obj) == mark_bit);
-  ASSERT(obj->Size() >= 2*kPointerSize);
-  ASSERT(IsMarking());
   Marking::WhiteToGrey(mark_bit);
 }