WebGL: Be less aggressive about pruning image backed mailboxes.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp

 /*
  * Copyright (c) 2010, 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 373 matching lines @@
     // Ensure not to call the destructor until deleteMailbox() is completed.
     RefPtr<DrawingBuffer> self = this;
     deleteMailbox(mailbox);
 }
 
 PassRefPtr<DrawingBuffer::MailboxInfo> DrawingBuffer::recycledMailbox()
 {
     if (m_recycledMailboxQueue.isEmpty())
         return PassRefPtr<MailboxInfo>();
 
+    // Creation of image backed mailboxes is very expensive, so be less
+    // aggressive about pruning them.
+    size_t cacheLimit = 1;
+    if (RuntimeEnabledFeatures::webGLImageChromiumEnabled())
+        cacheLimit = 4;
+
     WebExternalTextureMailbox mailbox;
-    while (!m_recycledMailboxQueue.isEmpty()) {
+    while (m_recycledMailboxQueue.size() > cacheLimit) {
         mailbox = m_recycledMailboxQueue.takeLast();
-        // Never have more than one mailbox in the released state.
-        if (!m_recycledMailboxQueue.isEmpty())
-            deleteMailbox(mailbox);
+        deleteMailbox(mailbox);
     }
+    mailbox = m_recycledMailboxQueue.takeLast();
 
     RefPtr<MailboxInfo> mailboxInfo;
     for (size_t i = 0; i < m_textureMailboxes.size(); i++) {
         if (nameEquals(m_textureMailboxes[i]->mailbox, mailbox)) {
             mailboxInfo = m_textureMailboxes[i];
             break;
         }
     }
     ASSERT(mailboxInfo);
 
@@ skipping 668 matching lines @@
 
 void DrawingBuffer::restoreTextureBindings()
 {
     // This class potentially modifies the bindings for GL_TEXTURE_2D and
     // GL_TEXTURE_RECTANGLE. Only GL_TEXTURE_2D needs to be restored since
     // the public interface for WebGL does not support GL_TEXTURE_RECTANGLE.
     m_gl->BindTexture(GL_TEXTURE_2D, m_texture2DBinding);
 }
 
 } // namespace blink