Detect discarded SkPictureShader pixel refs.

src/core/SkPictureShader.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPictureShader.h"
 
 #include "SkBitmap.h"
@@ skipping 59 matching lines @@
     virtual const Key& getKey() const SK_OVERRIDE { return fKey; }
     virtual size_t bytesUsed() const SK_OVERRIDE {
         return sizeof(fKey) + sizeof(SkShader) + fBitmapBytes;
     }
 
     static bool Visitor(const SkResourceCache::Rec& baseRec, void* contextShader) {
         const BitmapShaderRec& rec = static_cast<const BitmapShaderRec&>(baseRec);
         SkAutoTUnref<SkShader>* result = reinterpret_cast<SkAutoTUnref<SkShader>*>(contextShader);
 
         result->reset(SkRef(rec.fShader.get()));
-        return true;
+
+        SkBitmap tile;
+        rec.fShader.get()->asABitmap(&tile, NULL, NULL);
+        // FIXME: this doesn't protect the pixels from being discarded as soon as we unlock.
+        // Should be handled via a pixel ref generator instead
+        // (https://code.google.com/p/skia/issues/detail?id=3220).
+        SkAutoLockPixels alp(tile, true);
+        return tile.getPixels() != NULL;
     }
 };
 
 static bool cache_try_alloc_pixels(SkBitmap* bitmap) {
     SkBitmap::Allocator* allocator = SkResourceCache::GetAllocator();
 
     return NULL != allocator
         ? allocator->allocPixelRef(bitmap, NULL)
         : bitmap->tryAllocPixels();
 }
@@ skipping 197 matching lines @@
     }
     return bitmapShader->asFragmentProcessor(context, paint, NULL, paintColor, fp);
 }
 #else
 bool SkPictureShader::asFragmentProcessor(GrContext*, const SkPaint&, const SkMatrix*, GrColor*,
                                           GrFragmentProcessor**) const {
     SkDEBUGFAIL("Should not call in GPU-less build");
     return false;
 }
 #endif