Fix the speeling of "purgeable" in Gr code

src/lazy/SkDiscardablePixelRef.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDiscardablePixelRef.h"
 #include "SkDiscardableMemory.h"
 #include "SkImageGenerator.h"
@@ skipping 53 matching lines @@
     SkPMColor colors[256];
     int colorCount = 0;
 
     if (!fGenerator->getPixels(info, pixels, fRowBytes, colors, &colorCount)) {
         fDiscardableMemory->unlock();
         SkDELETE(fDiscardableMemory);
         fDiscardableMemory = NULL;
         return false;
     }
 
-    // Note: our ctable is not purgable, as it is not stored in the discardablememory block.
+    // Note: our ctable is not purgeable, as it is not stored in the discardablememory block.
     // This is because SkColorTable is refcntable, and therefore our caller could hold onto it
     // beyond the scope of a lock/unlock. If we change the API/lifecycle for SkColorTable, we
     // could move it into the block, but then again perhaps it is small enough that this doesn't
     // really matter.
     if (colorCount > 0) {
         fCTable.reset(SkNEW_ARGS(SkColorTable, (colors, colorCount)));
     } else {
         fCTable.reset(NULL);
     }
 
@@ skipping 34 matching lines @@
 // These are the public API
 
 bool SkInstallDiscardablePixelRef(SkImageGenerator* generator, SkBitmap* dst) {
     return SkInstallDiscardablePixelRef(generator, dst, NULL);
 }
 
 bool SkInstallDiscardablePixelRef(SkData* encoded, SkBitmap* dst) {
     SkImageGenerator* generator = SkImageGenerator::NewFromData(encoded);
     return generator ? SkInstallDiscardablePixelRef(generator, dst, NULL) : false;
 }