Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/WebGLCompressedTextureATC.h

Index: Source/core/html/canvas/WebGLCompressedTextureATC.h
diff --git a/Source/core/html/canvas/WebGLCompressedTextureATC.h b/Source/core/html/canvas/WebGLCompressedTextureATC.h
index 4856580fd0e4c4f8c13780026586711b2afad107..6cf65411c4fc0402b3cae5cf13f83b57799b1e28 100644
--- a/Source/core/html/canvas/WebGLCompressedTextureATC.h
+++ b/Source/core/html/canvas/WebGLCompressedTextureATC.h
@@ -29,7 +29,7 @@
 #include "bindings/v8/ScriptWrappable.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/html/canvas/WebGLExtension.h"
-#include "wtf/PassOwnPtr.h"
+#include "wtf/PassRefPtr.h"
 
 namespace WebCore {
 
@@ -37,7 +37,7 @@ class WebGLTexture;
 
 class WebGLCompressedTextureATC : public WebGLExtension, public ScriptWrappable {
 public:
-    static PassOwnPtr<WebGLCompressedTextureATC> create(WebGLRenderingContext*);
+    static PassRefPtr<WebGLCompressedTextureATC> create(WebGLRenderingContext*);
     static bool supported(WebGLRenderingContext*);
     static const char* getExtensionName();