Fix the context loss issue when switching tabs after enabled Canvas2D hardware acceleration

Source/platform/graphics/Canvas2DLayerBridge.cpp

 /*
  * Copyright (C) 2012 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 255 matching lines @@
 }
 
 bool Canvas2DLayerBridge::hasReleasedMailbox() const
 {
     return m_releasedMailboxInfoIndex != InvalidMailboxIndex;
 }
 
 void Canvas2DLayerBridge::freeReleasedMailbox()
 {
     MailboxInfo* mailboxInfo = releasedMailboxInfo();
+    m_lastImageId = -1;

[boliu, 2014/02/11 19:29:41]

We only want to do this if the released mailbox matches m_lastImageId. You can
do this by comparing m_lastImageId to mailboxInfo->SkImage->uniqueID(),
obviously with all the proper null checks in place.

Also released here means calling Canvas2DLayerBridge::mailboxReleased (ie
release back to us by compositor), not here, actually freeing the mailbox. So
move this to Canvas2DLayerBridge::mailboxReleased.

     if (!mailboxInfo)
         return;
 
     ASSERT(mailboxInfo->m_status == MailboxReleased);
     if (mailboxInfo->m_mailbox.syncPoint) {
         context()->waitSyncPoint(mailboxInfo->m_mailbox.syncPoint);
         mailboxInfo->m_mailbox.syncPoint = 0;
     }
     // Invalidate texture state in case the compositor altered it since the copy-on-write.
     if (mailboxInfo->m_image) {
@@ skipping 73 matching lines @@
     webContext->makeContextCurrent();
     flush();
 
     RefPtr<SkImage> image = adoptRef(m_canvas->newImageSnapshot());
 
     // Early exit if canvas was not drawn to since last prepareMailbox
     if (image->uniqueID() == m_lastImageId)
         return false;
     m_lastImageId = image->uniqueID();
 
     MailboxInfo* mailboxInfo = createMailboxInfo();

[boliu, 2014/02/11 19:29:41]

Here, will need to check if there is already a mailbox with matching uniqueID.
If there is, re-use the mailbox and not create another one.

     mailboxInfo->m_status = MailboxInUse;
     mailboxInfo->m_image = image;
 
     // Because of texture sharing with the compositor, we must invalidate
     // the state cached in skia so that the deferred copy on write
     // in SkSurface_Gpu does not make any false assumptions.
     mailboxInfo->m_image->getTexture()->invalidateCachedState();
 
     ASSERT(mailboxInfo->m_mailbox.syncPoint == 0);
     ASSERT(mailboxInfo->m_image.get());
@@ skipping 108 matching lines @@
 Canvas2DLayerBridge::MailboxInfo::MailboxInfo(const MailboxInfo& other) {
     // This copy constructor should only be used for Vector reallocation
     // Assuming 'other' is to be destroyed, we transfer m_image ownership
     // rather than do a refcount dance.
     memcpy(&m_mailbox, &other.m_mailbox, sizeof(m_mailbox));
     m_image = const_cast<MailboxInfo*>(&other)->m_image.release();
     m_status = other.m_status;
 }
 
 }