Implemented the RoundInt64ToFloat32 TurboFan operator for x64, arm64, and mips64.

src/compiler/mips64/code-generator-mips64.cc

Index: src/compiler/mips64/code-generator-mips64.cc
diff --git a/src/compiler/mips64/code-generator-mips64.cc b/src/compiler/mips64/code-generator-mips64.cc
index 24a3fa6ccd899863e94988ee83b14323564134e5..787c8fa32d373e7978979f412879994e56d2a20e 100644
--- a/src/compiler/mips64/code-generator-mips64.cc
+++ b/src/compiler/mips64/code-generator-mips64.cc
@@ -857,6 +857,12 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ cvt_d_w(i.OutputDoubleRegister(), scratch);
       break;
     }
+    case kMips64CvtSL: {
+      FPURegister scratch = kScratchDoubleReg;
+      __ dmtc1(i.InputRegister(0), scratch);
+      __ cvt_s_l(i.OutputDoubleRegister(), scratch);
+      break;
+    }
     case kMips64CvtDL: {
       FPURegister scratch = kScratchDoubleReg;
       __ dmtc1(i.InputRegister(0), scratch);