[compiler] Introduce code stubs for string relational comparisons.

src/crankshaft/mips64/lithium-codegen-mips64.cc

Index: src/crankshaft/mips64/lithium-codegen-mips64.cc
diff --git a/src/crankshaft/mips64/lithium-codegen-mips64.cc b/src/crankshaft/mips64/lithium-codegen-mips64.cc
index 721605aca98fb88e763cf6a7e40b5d26bc808235..21fe3ce9b085a5632df84b87a0ba2d6a23e272d1 100644
--- a/src/crankshaft/mips64/lithium-codegen-mips64.cc
+++ b/src/crankshaft/mips64/lithium-codegen-mips64.cc
@@ -2392,19 +2392,10 @@ void LCodeGen::DoStringCompareAndBranch(LStringCompareAndBranch* instr) {
   DCHECK(ToRegister(instr->left()).is(a1));
   DCHECK(ToRegister(instr->right()).is(a0));
 
-  if (Token::IsOrderedRelationalCompareOp(instr->op())) {
-    Handle<Code> code = CodeFactory::StringCompare(isolate()).code();
-    CallCode(code, RelocInfo::CODE_TARGET, instr);
-
-    EmitBranch(instr, ComputeCompareCondition(instr->op()), v0,
-               Operand(zero_reg));
-  } else {
-    Handle<Code> code = CodeFactory::StringEqual(isolate()).code();
-    CallCode(code, RelocInfo::CODE_TARGET, instr);
-    __ LoadRoot(at, Heap::kTrueValueRootIndex);
-
-    EmitBranch(instr, ComputeCompareCondition(instr->op()), v0, Operand(at));
-  }
+  Handle<Code> code = CodeFactory::StringCompare(isolate(), instr->op()).code();
+  CallCode(code, RelocInfo::CODE_TARGET, instr);
+  __ LoadRoot(at, Heap::kTrueValueRootIndex);
+  EmitBranch(instr, eq, v0, Operand(at));
 }