[turbofan] Introduce dedicated CallFrequency class.

src/compiler/js-inlining-heuristic.h

Index: src/compiler/js-inlining-heuristic.h
diff --git a/src/compiler/js-inlining-heuristic.h b/src/compiler/js-inlining-heuristic.h
index b834cb0a06ba07a3483dba73f6201b931dee8789..b11a087560164d2e64abbc1dca2ba18a7666e471 100644
--- a/src/compiler/js-inlining-heuristic.h
+++ b/src/compiler/js-inlining-heuristic.h
@@ -43,8 +43,8 @@ class JSInliningHeuristic final : public AdvancedReducer {
     // we use {num_functions == 1 && functions[0].is_null()} as an indicator.
     Handle<SharedFunctionInfo> shared_info;
     int num_functions;
-    Node* node = nullptr;    // The call site at which to inline.
-    float frequency = 0.0f;  // Relative frequency of this call site.
+    Node* node = nullptr;     // The call site at which to inline.
+    CallFrequency frequency;  // Relative frequency of this call site.
   };
 
   // Comparator for candidates.