ARM: Support record write stubs for incremental marking.

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index 4d86e225693aa49a0a44a492ce94770a44febfb9..0aac220a66e64553308af9561bceb9d198f92119 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -439,10 +439,11 @@ void MacroAssembler::RecordWriteField(
   // of the object, so so offset must be a multiple of kPointerSize.
   ASSERT(IsAligned(offset, kPointerSize));
 
-  add(dst, object, Operand(offset));
+  add(dst, object, Operand(offset - kHeapObjectTag));
   if (emit_debug_code()) {
     Label ok;
-    JumpIfNotSmi(dst, &ok);
+    tst(dst, Operand((1 << kPointerSizeLog2) - 1));
+    b(eq, &ok);
     stop("Unaligned cell in write barrier");
     bind(&ok);
   }