ensure that we call onUnlock only when we onLock succeeded

src/core/SkScaledImageCache.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 "SkScaledImageCache.h"
 #include "SkMipMap.h"
 #include "SkOnce.h"
@@ skipping 191 matching lines @@
     virtual void* onLockPixels(SkColorTable**) SK_OVERRIDE;
     virtual void onUnlockPixels() SK_OVERRIDE;
     virtual size_t getAllocatedSizeInBytes() const SK_OVERRIDE;
 
 private:
     SkImageInfo fInfo;  // remove when SkPixelRef gets this in baseclass
 
     SkDiscardableMemory* fDM;
     size_t               fRB;
     bool                 fFirstTime;
-    bool                 fIsLocked;
 
     typedef SkPixelRef INHERITED;
 };
 
 SkOneShotDiscardablePixelRef::SkOneShotDiscardablePixelRef(const SkImageInfo& info,
                                              SkDiscardableMemory* dm,
                                              size_t rowBytes)
     : INHERITED(info)
     , fDM(dm)
     , fRB(rowBytes)
 {
     fInfo = info;   // remove this redundant field when SkPixelRef has info
 
     SkASSERT(dm->data());
     fFirstTime = true;
-    fIsLocked = false;
 }
 
 SkOneShotDiscardablePixelRef::~SkOneShotDiscardablePixelRef() {
     SkDELETE(fDM);
 }
 
 void* SkOneShotDiscardablePixelRef::onLockPixels(SkColorTable** ctable) {
     if (fFirstTime) {
         // we're already locked
+        SkASSERT(fDM->data());
         fFirstTime = false;
         return fDM->data();
     }
-
-    SkASSERT(!fIsLocked);
-    fIsLocked = fDM->lock();
-    return fIsLocked ? fDM->data() : NULL;
+    return fDM->lock() ? fDM->data() : NULL;
 }
 
 void SkOneShotDiscardablePixelRef::onUnlockPixels() {
     SkASSERT(!fFirstTime);
-    if (fIsLocked) {
-        fIsLocked = false;
-        fDM->unlock();
-    }
+    fDM->unlock();
 }
 
 size_t SkOneShotDiscardablePixelRef::getAllocatedSizeInBytes() const {
     return fInfo.fHeight * fRB;
 }
 
 class SkScaledImageCacheDiscardableAllocator : public SkBitmap::Allocator {
 public:
     SkScaledImageCacheDiscardableAllocator(
                             SkScaledImageCache::DiscardableFactory factory) {
@@ skipping 498 matching lines @@
     return SkScaledImageCache::GetBytesUsed();
 }
 
 size_t SkGraphics::GetImageCacheByteLimit() {
     return SkScaledImageCache::GetByteLimit();
 }
 
 size_t SkGraphics::SetImageCacheByteLimit(size_t newLimit) {
     return SkScaledImageCache::SetByteLimit(newLimit);
 }