[turbofan] Separate JSInliningHeuristic into own class.

src/compiler/js-inlining.h

Index: src/compiler/js-inlining.h
diff --git a/src/compiler/js-inlining.h b/src/compiler/js-inlining.h
index 21057e61e40612154c61f75e6d81614263eb770e..a77dceb3342da48791ea7b098c3e32fdf4960e98 100644
--- a/src/compiler/js-inlining.h
+++ b/src/compiler/js-inlining.h
@@ -19,22 +19,26 @@ namespace compiler {
 // Forward declarations.
 class JSCallFunctionAccessor;
 
+// The JSInliner provides the core graph inlining machinery. Note that this
+// class only deals with the mechanics of how to inline one graph into another,
+// heuristics that decide what and how much to inline are beyond its scope.
 class JSInliner final : public AdvancedReducer {
  public:
-  enum Mode { kRestrictedInlining, kGeneralInlining };
-
-  JSInliner(Editor* editor, Mode mode, Zone* local_zone, CompilationInfo* info,
+  JSInliner(Editor* editor, Zone* local_zone, CompilationInfo* info,
             JSGraph* jsgraph)
       : AdvancedReducer(editor),
-        mode_(mode),
         local_zone_(local_zone),
         info_(info),
         jsgraph_(jsgraph) {}
 
+  // Reducer interface, eagerly inlines everything.
   Reduction Reduce(Node* node) final;
 
+  // Can be used by inlining heuristics or by testing code directly, without
+  // using the above generic reducer interface of the inlining machinery.
+  Reduction ReduceJSCallFunction(Node* node, Handle<JSFunction> function);
+
  private:
-  Mode const mode_;
   Zone* local_zone_;
   CompilationInfo* info_;
   JSGraph* jsgraph_;