A64: Update DoAllocate() to use a W register for the size

src/a64/macro-assembler-a64.cc

Index: src/a64/macro-assembler-a64.cc
diff --git a/src/a64/macro-assembler-a64.cc b/src/a64/macro-assembler-a64.cc
index 1e8da54314a5fa2434071cb051a8281126f38301..e3561a160e7906e16aeb71357cb8014a562eb952 100644
--- a/src/a64/macro-assembler-a64.cc
+++ b/src/a64/macro-assembler-a64.cc
@@ -3071,7 +3071,7 @@ void MacroAssembler::Allocate(Register object_size,
   }
 
   ASSERT(!AreAliased(object_size, result, scratch1, scratch2, Tmp0(), Tmp1()));
-  ASSERT(object_size.Is64Bits() && result.Is64Bits() && scratch1.Is64Bits() &&
+  ASSERT(result.Is64Bits() && scratch1.Is64Bits() &&
          scratch2.Is64Bits() && Tmp0().Is64Bits() && Tmp1().Is64Bits());
 
   // Check relative positions of allocation top and limit addresses.