Fix mistake in ARM version of string length stub.

src/ic-arm.cc

Index: src/ic-arm.cc
===================================================================
--- src/ic-arm.cc	(revision 605)
+++ src/ic-arm.cc	(working copy)
@@ -174,12 +174,13 @@
   // Check that the object is a string.
   __ ldr(r1, FieldMemOperand(r0, HeapObject::kMapOffset));
   __ ldrb(r1, FieldMemOperand(r1, Map::kInstanceTypeOffset));
+  __ mov(r3, Operand(r1));
   __ and_(r1, r1, Operand(kIsNotStringMask));
   // The cast is to resolve the overload for the argument of 0x0.
   __ cmp(r1, Operand(static_cast<int32_t>(kStringTag)));
   __ b(ne, &miss);
 
-  __ and_(r1, r1, Operand(kStringSizeMask));
+  __ and_(r1, r3, Operand(kStringSizeMask));
   __ add(r1, r1, Operand(String::kHashShift));
   // Load length directly from the string.
   __ ldr(r0, FieldMemOperand(r0, String::kLengthOffset));