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 421 matching lines @@
 
 void Canvas2DLayerBridge::mailboxReleased(const blink::WebExternalTextureMailbox& mailbox)
 {
     freeReleasedMailbox(); // Never have more than one mailbox in the released state.
     Vector<MailboxInfo>::iterator mailboxInfo;
     for (mailboxInfo = m_mailboxes.begin(); mailboxInfo < m_mailboxes.end(); ++mailboxInfo) {
         if (!memcmp(mailboxInfo->m_mailbox.name, mailbox.name, sizeof(mailbox.name))) {
             mailboxInfo->m_mailbox.syncPoint = mailbox.syncPoint;
             ASSERT(mailboxInfo->m_status == MailboxInUse);
             mailboxInfo->m_status = MailboxReleased;
+            resetLastImageIdIfNecessary();
             // Trigger Canvas2DLayerBridge self-destruction if this is the
             // last live mailbox and the layer bridge is not externally
             // referenced.
             m_releasedMailboxInfoIndex = mailboxInfo - m_mailboxes.begin();
             m_framesSinceMailboxRelease = 0;
             if (isHidden()) {
                 freeReleasedMailbox();
             } else {
                 ASSERT(!m_destructionInProgress);
                 Canvas2DLayerManager::get().layerTransientResourceAllocationChanged(this);
             }
             ASSERT(mailboxInfo->m_parentLayerBridge.get() == this);
             mailboxInfo->m_parentLayerBridge.clear();
             return;
         }
     }
 }
 
+void Canvas2DLayerBridge::resetLastImageIdIfNecessary()
+{
+    Vector<MailboxInfo>::iterator mailboxInfo;
+    for (mailboxInfo = m_mailboxes.begin(); mailboxInfo < m_mailboxes.end(); ++mailboxInfo) {

[Justin Novosad, 2014/02/13 15:32:18]

You can do the check in O(1) time instead of O(N) if you add a new data member
m_activeMailboxCount. You initialize it to zero, increment it in prepareMailbox,
decrement in mailboxReleased.

+        if (mailboxInfo->m_status == MailboxInUse)
+            return;
+    }
+    m_lastImageId = 0;
+}
+
 blink::WebLayer* Canvas2DLayerBridge::layer() const
 {
     ASSERT(m_layer);
     return m_layer->layer();
 }
 
 void Canvas2DLayerBridge::willUse()
 {
     ASSERT(!m_destructionInProgress);
     Canvas2DLayerManager::get().layerDidDraw(this);
@@ skipping 18 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;
 }
 
 }