Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/WebGLDepthTexture.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 17 matching lines @@
 #include "core/html/canvas/WebGLDepthTexture.h"
 
 #include "core/platform/graphics/Extensions3D.h"
 
 namespace WebCore {
 
 WebGLDepthTexture::WebGLDepthTexture(WebGLRenderingContext* context)
     : WebGLExtension(context)
 {
     ScriptWrappable::init(this);
-    context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_CHROMIUM_depth_texture");
+    enable();
 }
 
 WebGLDepthTexture::~WebGLDepthTexture()
 {
 }
 
+void WebGLDepthTexture::enable()
+{
+    m_context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_CHROMIUM_depth_texture");
+}
+
 WebGLExtension::ExtensionName WebGLDepthTexture::getName() const
 {
     return WebGLDepthTextureName;
 }
 
 PassOwnPtr<WebGLDepthTexture> WebGLDepthTexture::create(WebGLRenderingContext* context)
 {
     return adoptPtr(new WebGLDepthTexture(context));
 }
 
 bool WebGLDepthTexture::supported(WebGLRenderingContext* context)
 {
     Extensions3D* extensions = context->graphicsContext3D()->getExtensions();
     return extensions->supports("GL_CHROMIUM_depth_texture")
         || extensions->supports("GL_OES_depth_texture")
         || extensions->supports("GL_ARB_depth_texture");
 }
 
 const char* WebGLDepthTexture::getExtensionName()
 {
     return "WEBGL_depth_texture";
 }
 
 } // namespace WebCore