Add MakeEmpty to GrIRect16

include/gpu/GrRect.h

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrRect_DEFINED
 #define GrRect_DEFINED
 
 #include "SkTypes.h"
 #include "SkRect.h"
 
 struct GrIRect16 {
     int16_t fLeft, fTop, fRight, fBottom;
 
+    static GrIRect16 SK_WARN_UNUSED_RESULT MakeEmpty() {
+        GrIRect16 r;
+        r.setEmpty();
+        return r;
+    }
+
     int width() const { return fRight - fLeft; }
     int height() const { return fBottom - fTop; }
     int area() const { return this->width() * this->height(); }
     bool isEmpty() const { return fLeft >= fRight || fTop >= fBottom; }
 
+    void setEmpty() { memset(this, 0, sizeof(*this)); }
+
     void set(const SkIRect& r) {
         fLeft   = SkToS16(r.fLeft);
         fTop    = SkToS16(r.fTop);
         fRight  = SkToS16(r.fRight);
         fBottom = SkToS16(r.fBottom);
     }
 };
 
 #endif