[compiler] Introduce code stubs for string relational comparisons.

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

Index: src/crankshaft/mips/lithium-codegen-mips.cc
diff --git a/src/crankshaft/mips/lithium-codegen-mips.cc b/src/crankshaft/mips/lithium-codegen-mips.cc
index dd908dea5ca3c9c15ee965c831148091bc1bfcfc..b32bce842581073cf35cbeb92c8901bda67e6778 100644
--- a/src/crankshaft/mips/lithium-codegen-mips.cc
+++ b/src/crankshaft/mips/lithium-codegen-mips.cc
@@ -2275,19 +2275,10 @@ 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));
 }