Fix ref counting of cached layer's texture

src/gpu/GrLayerCache.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrLayerCache_DEFINED
 #define GrLayerCache_DEFINED
 
@@ skipping 64 matching lines @@
     // GrCachedLayer proper
     GrCachedLayer(uint32_t pictureID, int layerID) 
         : fKey(pictureID, layerID)
         , fTexture(NULL)
         , fRect(GrIRect16::MakeEmpty())
         , fPlot(NULL)
         , fLocked(false) {
         SkASSERT(SK_InvalidGenID != pictureID && layerID >= 0);
     }
 
+    ~GrCachedLayer() {
+        SkSafeUnref(fTexture);
+    }
+
     uint32_t pictureID() const { return fKey.getPictureID(); }
     int layerID() const { return fKey.getLayerID(); }
 
-    // This call takes over the caller's ref
     void setTexture(GrTexture* texture, const GrIRect16& rect) {
-        if (NULL != fTexture) {
-            fTexture->unref();
-        }
-
-        fTexture = texture; // just take over caller's ref
+        SkRefCnt_SafeAssign(fTexture, texture);
         fRect = rect;
     }
     GrTexture* texture() { return fTexture; }
     const GrIRect16& rect() const { return fRect; }
 
     void setPlot(GrPlot* plot) {
         SkASSERT(NULL == fPlot);
         fPlot = plot;
     }
     GrPlot* plot() { return fPlot; }
@@ skipping 114 matching lines @@
     // Try to find a purgeable plot and clear it out. Return true if a plot
     // was purged; false otherwise.
     bool purgePlot();
 
     // for testing
     friend class TestingAccess;
     int numLayers() const { return fLayerHash.count(); }
 };
 
 #endif