Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/WebGLExtension.h

 /*
  * 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:
  *
  * 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 41 matching lines @@
         WebGLDepthTextureName,
         WebGLLoseContextName,
     };
 
     void ref() { m_context->ref(); }
     void deref() { m_context->deref(); }
     WebGLRenderingContext* context() { return m_context; }
 
     virtual ~WebGLExtension();
     virtual ExtensionName getName() const = 0;
+    virtual void enable() = 0;
+
+    void restore()

[Ken Russell (switch to Gerrit), 2013/06/05 00:46:38]

Is a restore() method needed? As I understand it, when the context is lost (even
via WEBGL_lose_context), all of the extension objects (except for
WEBGL_lose_context) are permanently lost, and further, disassociated from the
WebGLRenderingContext -- so if the context is restored, and the extension is
fetched again, a different JavaScript object will be returned. If this is
correct then restore() can be removed.

+    {
+        m_lost = false;
+        enable();
+    }
+
+    virtual void lose()
+    {
+        m_lost = true;
+    }
+
+    bool isLost()
+    {
+        return m_lost || m_context->isContextLost();
+    }
 
 protected:
     WebGLExtension(WebGLRenderingContext*);
+
     WebGLRenderingContext* m_context;
+    bool m_lost;

[Ken Russell (switch to Gerrit), 2013/06/05 00:46:38]

Should m_lost be private instead?

+
 };
 
 } // namespace WebCore
 
 #endif // WebGLExtension_h