[turbofan] Introduce dedicated CallFrequency class.

src/compiler/js-operator.cc

Index: src/compiler/js-operator.cc
diff --git a/src/compiler/js-operator.cc b/src/compiler/js-operator.cc
index 9b53d4bb54bb92e48a82bbe467c3cf0cad940b63..1e2c15882b2f52a471574e460bb2b91b1e60027b 100644
--- a/src/compiler/js-operator.cc
+++ b/src/compiler/js-operator.cc
@@ -17,6 +17,11 @@ namespace v8 {
 namespace internal {
 namespace compiler {
 
+std::ostream& operator<<(std::ostream& os, CallFrequency f) {
+  if (f.IsUnknown()) return os << "unknown";
+  return os << f.value();
+}
+
 VectorSlotPair::VectorSlotPair() {}
 
 
@@ -747,7 +752,7 @@ const Operator* JSOperatorBuilder::CallForwardVarargs(
       parameters);                                               // parameter
 }
 
-const Operator* JSOperatorBuilder::Call(size_t arity, float frequency,
+const Operator* JSOperatorBuilder::Call(size_t arity, CallFrequency frequency,
                                         VectorSlotPair const& feedback,
                                         ConvertReceiverMode convert_mode,
                                         TailCallMode tail_call_mode) {
@@ -793,7 +798,8 @@ const Operator* JSOperatorBuilder::CallRuntime(const Runtime::Function* f,
       parameters);                                        // parameter
 }
 
-const Operator* JSOperatorBuilder::Construct(uint32_t arity, float frequency,
+const Operator* JSOperatorBuilder::Construct(uint32_t arity,
+                                             CallFrequency frequency,
                                              VectorSlotPair const& feedback) {
   ConstructParameters parameters(arity, frequency, feedback);
   return new (zone()) Operator1<ConstructParameters>(   // --