Support string add in crankshaft:

src/arm/code-stubs-arm.cc

Index: src/arm/code-stubs-arm.cc
diff --git a/src/arm/code-stubs-arm.cc b/src/arm/code-stubs-arm.cc
index d77047fc0bfd79a23cea2ce3067750d543b210ad..d66daea0a0aa7f751f3854a72a91ac01eb48fa0c 100644
--- a/src/arm/code-stubs-arm.cc
+++ b/src/arm/code-stubs-arm.cc
@@ -1817,6 +1817,9 @@ void TypeRecordingBinaryOpStub::Generate(MacroAssembler* masm) {
     case TRBinaryOpIC::ODDBALL:
       GenerateOddballStub(masm);
       break;
+    case TRBinaryOpIC::BOTH_STRING:
+      GenerateBothStringStub(masm);
+      break;
     case TRBinaryOpIC::STRING:
       GenerateStringStub(masm);
       break;
@@ -2257,6 +2260,36 @@ void TypeRecordingBinaryOpStub::GenerateStringStub(MacroAssembler* masm) {
 }
 
 
+void TypeRecordingBinaryOpStub::GenerateBothStringStub(MacroAssembler* masm) {
+  Label call_runtime;
+  ASSERT(operands_type_ == TRBinaryOpIC::BOTH_STRING);
+  ASSERT(op_ == Token::ADD);
+  // If both arguments are strings, call the string add stub.
+  // Otherwise, do a transition.
+
+  // Registers containing left and right operands respectively.
+  Register left = r1;
+  Register right = r0;
+
+  // Test if left operand is a string.
+  __ JumpIfSmi(left, &call_runtime);
+  __ CompareObjectType(left, r2, r2, FIRST_NONSTRING_TYPE);
+  __ b(ge, &call_runtime);
+
+  // Test if right operand is a string.
+  __ JumpIfSmi(right, &call_runtime);
+  __ CompareObjectType(right, r2, r2, FIRST_NONSTRING_TYPE);
+  __ b(ge, &call_runtime);
+
+  StringAddStub string_add_stub(NO_STRING_CHECK_IN_STUB);
+  GenerateRegisterArgsPush(masm);
+  __ TailCallStub(&string_add_stub);
+
+  __ bind(&call_runtime);
+  GenerateTypeTransition(masm);
+}
+
+
 void TypeRecordingBinaryOpStub::GenerateInt32Stub(MacroAssembler* masm) {
   ASSERT(operands_type_ == TRBinaryOpIC::INT32);