[turbofan] Add support for Math.round to the JSBuiltinReducer.

src/compiler/js-builtin-reducer.h

Index: src/compiler/js-builtin-reducer.h
diff --git a/src/compiler/js-builtin-reducer.h b/src/compiler/js-builtin-reducer.h
index cfacdc1e8c387a3c3493553faac04e27276da41c..b64b33565de5c5f7455d441d849575cf9d202ff3 100644
--- a/src/compiler/js-builtin-reducer.h
+++ b/src/compiler/js-builtin-reducer.h
@@ -9,6 +9,10 @@
 
 namespace v8 {
 namespace internal {
+
+// Forward declarations.
+class TypeCache;
+
 namespace compiler {
 
 // Forward declarations.
@@ -30,6 +34,7 @@ class JSBuiltinReducer final : public AdvancedReducer {
   Reduction ReduceMathMax(Node* node);
   Reduction ReduceMathImul(Node* node);
   Reduction ReduceMathFround(Node* node);
+  Reduction ReduceMathRound(Node* node);
 
   Graph* graph() const;
   JSGraph* jsgraph() const { return jsgraph_; }
@@ -38,7 +43,8 @@ class JSBuiltinReducer final : public AdvancedReducer {
   MachineOperatorBuilder* machine() const;
   SimplifiedOperatorBuilder* simplified() const;
 
-  JSGraph* jsgraph_;
+  JSGraph* const jsgraph_;
+  TypeCache const& type_cache_;
 };
 
 }  // namespace compiler