Get rid of unused STRING_ADD_ERECT_FRAME flag.

src/mips/code-stubs-mips.cc

Index: src/mips/code-stubs-mips.cc
diff --git a/src/mips/code-stubs-mips.cc b/src/mips/code-stubs-mips.cc
index 4e19f1d97f5c1ca2e77587016f6938937d936867..e334b2896eb2f6a3aeee4a9baf6f76d034d3f0fa 100644
--- a/src/mips/code-stubs-mips.cc
+++ b/src/mips/code-stubs-mips.cc
@@ -4781,33 +4781,11 @@ void StringAddStub::Generate(MacroAssembler* masm) {
 
   // Just jump to runtime to add the two strings.
   __ bind(&call_runtime);
-  if ((flags_ & STRING_ADD_ERECT_FRAME) != 0) {
-    GenerateRegisterArgsPop(masm);
-    // Build a frame.
-    {
-      FrameScope scope(masm, StackFrame::INTERNAL);
-      GenerateRegisterArgsPush(masm);
-      __ CallRuntime(Runtime::kStringAdd, 2);
-    }
-    __ Ret();
-  } else {
-    __ TailCallRuntime(Runtime::kStringAdd, 2, 1);
-  }
+  __ TailCallRuntime(Runtime::kStringAdd, 2, 1);
 
   if (call_builtin.is_linked()) {
     __ bind(&call_builtin);
-    if ((flags_ & STRING_ADD_ERECT_FRAME) != 0) {
-      GenerateRegisterArgsPop(masm);
-      // Build a frame.
-      {
-        FrameScope scope(masm, StackFrame::INTERNAL);
-        GenerateRegisterArgsPush(masm);
-        __ InvokeBuiltin(builtin_id, CALL_FUNCTION);
-      }
-      __ Ret();
-    } else {
-      __ InvokeBuiltin(builtin_id, JUMP_FUNCTION);
-    }
+    __ InvokeBuiltin(builtin_id, JUMP_FUNCTION);
   }
 }