Use new SkBaseMutex::assertHeld() in DiscardableMemoryPool

src/lazy/SkDiscardableMemoryPool.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 "SkDiscardableMemory.h"
 #include "SkDiscardableMemoryPool.h"
 #include "SkLazyPtr.h"
@@ skipping 127 matching lines @@
     #endif  // SK_LAZY_CACHE_STATS
 }
 DiscardableMemoryPool::~DiscardableMemoryPool() {
     // PoolDiscardableMemory objects that belong to this pool are
     // always deleted before deleting this pool since each one has a
     // ref to the pool.
     SkASSERT(fList.isEmpty());
 }
 
 void DiscardableMemoryPool::dumpDownTo(size_t budget) {
-    // assert((NULL = fMutex) || fMutex->isLocked());
-    // TODO(halcanary) implement bool fMutex::isLocked().
-    // WARNING: only call this function after aquiring lock.
+    if (fMutex != NULL) {
+        fMutex->assertHeld();
+    }
     if (fUsed <= budget) {
         return;
     }
     typedef SkTInternalLList<PoolDiscardableMemory>::Iter Iter;
     Iter iter;
     PoolDiscardableMemory* cur = iter.init(fList, Iter::kTail_IterStart);
     while ((fUsed > budget) && (NULL != cur)) {
         if (!cur->fLocked) {
             PoolDiscardableMemory* dm = cur;
             SkASSERT(dm->fPointer != NULL);
@@ skipping 101 matching lines @@
 SkDiscardableMemoryPool* SkGetGlobalDiscardableMemoryPool() {
     SK_DECLARE_STATIC_LAZY_PTR(SkDiscardableMemoryPool, global, create_global_pool);
     return global.get();
 }
 
 // defined in SkImageGenerator.h
 void SkPurgeGlobalDiscardableMemoryPool() {
     SkGetGlobalDiscardableMemoryPool()->dumpPool();
 }
 ////////////////////////////////////////////////////////////////////////////////