[compiler] Introduce StringEqualStub and StringNotEqualStub.

src/crankshaft/arm64/lithium-codegen-arm64.cc

Index: src/crankshaft/arm64/lithium-codegen-arm64.cc
diff --git a/src/crankshaft/arm64/lithium-codegen-arm64.cc b/src/crankshaft/arm64/lithium-codegen-arm64.cc
index abb0e71ea419deb6623ab5300a91dd471582fdc4..6e9d604be8a074026a7f5e538330de3cd0b43be2 100644
--- a/src/crankshaft/arm64/lithium-codegen-arm64.cc
+++ b/src/crankshaft/arm64/lithium-codegen-arm64.cc
@@ -5193,10 +5193,18 @@ void LCodeGen::DoStringCompareAndBranch(LStringCompareAndBranch* instr) {
   DCHECK(ToRegister(instr->left()).is(x1));
   DCHECK(ToRegister(instr->right()).is(x0));
 
-  Handle<Code> code = CodeFactory::StringCompare(isolate()).code();
-  CallCode(code, RelocInfo::CODE_TARGET, instr);
+  if (Token::IsOrderedRelationalCompareOp(instr->op())) {
+    Handle<Code> code = CodeFactory::StringCompare(isolate()).code();
+    CallCode(code, RelocInfo::CODE_TARGET, instr);
+
+    EmitCompareAndBranch(instr, TokenToCondition(instr->op(), false), x0, 0);
+  } else {
+    Handle<Code> code = CodeFactory::StringEqual(isolate()).code();
+    CallCode(code, RelocInfo::CODE_TARGET, instr);
+    __ CompareRoot(x0, Heap::kTrueValueRootIndex);
 
-  EmitCompareAndBranch(instr, TokenToCondition(instr->op(), false), x0, 0);
+    EmitBranch(instr, TokenToCondition(instr->op(), false));
+  }
 }