Implemented the RoundUint64ToFloat64 TurboFan operator for x64 and arm64.

src/compiler/arm64/code-generator-arm64.cc

Index: src/compiler/arm64/code-generator-arm64.cc
diff --git a/src/compiler/arm64/code-generator-arm64.cc b/src/compiler/arm64/code-generator-arm64.cc
index 0915b7321d6feeb3b572a68971945c5e5ad36426..c6136a09db8bd9ae0e7ff1836dd5bd0af8918c5f 100644
--- a/src/compiler/arm64/code-generator-arm64.cc
+++ b/src/compiler/arm64/code-generator-arm64.cc
@@ -983,6 +983,9 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
     case kArm64Uint32ToFloat64:
       __ Ucvtf(i.OutputDoubleRegister(), i.InputRegister32(0));
       break;
+    case kArm64Uint64ToFloat64:
+      __ Ucvtf(i.OutputDoubleRegister(), i.InputRegister64(0));
+      break;
     case kArm64Float64ExtractLowWord32:
       __ Fmov(i.OutputRegister32(), i.InputFloat32Register(0));
       break;