[turbofan] Pull ResizeMergeOrPhi into CommonOperatorBuilder and use in ControlReducer.

src/compiler/common-operator.h

Index: src/compiler/common-operator.h
diff --git a/src/compiler/common-operator.h b/src/compiler/common-operator.h
index d61e110a12d6cbd4ec510b74196289e0c283aebd..1531b23e5fe8faf8e1076e4c1dd20a19c6b68717 100644
--- a/src/compiler/common-operator.h
+++ b/src/compiler/common-operator.h
@@ -201,6 +201,10 @@ class CommonOperatorBuilder FINAL : public ZoneObject {
   const Operator* Call(const CallDescriptor* descriptor);
   const Operator* Projection(size_t index);
 
+  // Constructs a new merge or phi operator with the same opcode as {op}, but
+  // with {size} inputs.
+  const Operator* ResizeMergeOrPhi(const Operator* op, int size);
+
  private:
   Zone* zone() const { return zone_; }