Fix leaks in DrawingBufferTest

Source/platform/graphics/gpu/DrawingBufferTest.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 244 matching lines @@
     // Prepare another mailbox and verify that it's the correct size.
     m_drawingBuffer->markContentsChanged();
     EXPECT_TRUE(m_drawingBuffer->prepareMailbox(&mailbox, 0));
     EXPECT_EQ(initialSize, webContext()->mostRecentlyProducedSize());
 
     // Prepare one final mailbox and verify that it's the correct size.
     m_drawingBuffer->mailboxReleased(mailbox, false);
     m_drawingBuffer->markContentsChanged();
     EXPECT_TRUE(m_drawingBuffer->prepareMailbox(&mailbox, 0));
     EXPECT_EQ(initialSize, webContext()->mostRecentlyProducedSize());
+    m_drawingBuffer->mailboxReleased(mailbox, false);
     m_drawingBuffer->beginDestruction();
 }
 
 TEST_F(DrawingBufferTest, verifyDestructionCompleteAfterAllMailboxesReleased)
 {
     bool live = true;
     m_drawingBuffer->m_live = &live;
 
     WebExternalTextureMailbox mailbox1;
     WebExternalTextureMailbox mailbox2;
@@ skipping 382 matching lines @@
     mailbox.syncPoint = waitSyncPoint;
     m_drawingBuffer->setIsHidden(true);
     m_drawingBuffer->mailboxReleased(mailbox);
     // m_drawingBuffer deletes mailbox immediately when hidden.
     EXPECT_EQ(waitSyncPoint, webContext()->mostRecentlyWaitedSyncPoint());
 
     m_drawingBuffer->beginDestruction();
 }
 
 } // namespace blink