Purge the SkLiteDL freelist when PurgeAllCaches() is called.

src/core/SkLiteDL.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkImageFilter.h"
@@ skipping 693 matching lines @@
         self->fBytes.rewind();
 
         SkAutoMutexAcquire lock(gFreeStackLock);
         self->fNext = gFreeStack;
         gFreeStack = self;
         return;
     }
 
     delete this;
 }
+
+void SkLiteDL::PurgeFreelist() {
+    SkAutoMutexAcquire lock(gFreeStackLock);
+    while (gFreeStack) {
+        SkLiteDL* top = gFreeStack;
+        gFreeStack = gFreeStack->fNext;
+        delete top;   // Calling unref() here would just put it back on the list!
+    }
+}