[turbofan] Implemented the optional Float32RoundDown operator.

src/compiler/arm64/instruction-selector-arm64.cc

Index: src/compiler/arm64/instruction-selector-arm64.cc
diff --git a/src/compiler/arm64/instruction-selector-arm64.cc b/src/compiler/arm64/instruction-selector-arm64.cc
index 841011efa5d6c73881908b05a204f1ffa42c0f34..6bdf7f232e785f15cb0337ba4adbde14863d506c 100644
--- a/src/compiler/arm64/instruction-selector-arm64.cc
+++ b/src/compiler/arm64/instruction-selector-arm64.cc
@@ -1473,6 +1473,11 @@ void InstructionSelector::VisitFloat64Sqrt(Node* node) {
 }
 
 
+void InstructionSelector::VisitFloat32RoundDown(Node* node) {
+  VisitRR(this, kArm64Float32RoundDown, node);
+}
+
+
 void InstructionSelector::VisitFloat64RoundDown(Node* node) {
   VisitRR(this, kArm64Float64RoundDown, node);
 }
@@ -2064,6 +2069,7 @@ MachineOperatorBuilder::Flags
 InstructionSelector::SupportedMachineOperatorFlags() {
   return MachineOperatorBuilder::kFloat32Max |
          MachineOperatorBuilder::kFloat32Min |
+         MachineOperatorBuilder::kFloat32RoundDown |
          MachineOperatorBuilder::kFloat64Max |
          MachineOperatorBuilder::kFloat64Min |
          MachineOperatorBuilder::kFloat64RoundDown |