Fix a potential crash bug in keyed calls for non-string keys.

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
===================================================================
--- src/arm/macro-assembler-arm.cc	(revision 6762)
+++ src/arm/macro-assembler-arm.cc	(working copy)
@@ -929,8 +929,8 @@
 
 
 void MacroAssembler::IsObjectJSStringType(Register object,
-                                           Register scratch,
-                                           Label* fail) {
+                                          Register scratch,
+                                          Label* fail) {
   ASSERT(kNotStringTag != 0);
 
   ldr(scratch, FieldMemOperand(object, HeapObject::kMapOffset));
@@ -2122,6 +2122,19 @@
 }
 
 
+void MacroAssembler::AbortIfNotString(Register object) {
+  STATIC_ASSERT(kSmiTag == 0);
+  tst(object, Operand(kSmiTagMask));
+  Assert(ne, "Operand is not a string");
+  push(object);
+  ldr(object, FieldMemOperand(object, HeapObject::kMapOffset));
+  CompareInstanceType(object, object, FIRST_NONSTRING_TYPE);
+  pop(object);
+  Assert(lo, "Operand is not a string");
+}
+
+
+
 void MacroAssembler::AbortIfNotRootValue(Register src,
                                          Heap::RootListIndex root_value_index,
                                          const char* message) {