Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/WebGLDebugShaders.h

Index: Source/core/html/canvas/WebGLDebugShaders.h
diff --git a/Source/core/html/canvas/WebGLDebugShaders.h b/Source/core/html/canvas/WebGLDebugShaders.h
index 67e2067b31b891975ac54096d6aa3741648b68a4..8c19c5a30c05d2fe042070ff11239db835eb1b79 100644
--- a/Source/core/html/canvas/WebGLDebugShaders.h
+++ b/Source/core/html/canvas/WebGLDebugShaders.h
@@ -28,7 +28,7 @@
 
 #include "bindings/v8/ScriptWrappable.h"
 #include "core/html/canvas/WebGLExtension.h"
-#include "wtf/PassOwnPtr.h"
+#include "wtf/PassRefPtr.h"
 
 namespace WebCore {
 
@@ -38,7 +38,7 @@ typedef int ExceptionCode;
 
 class WebGLDebugShaders : public WebGLExtension, public ScriptWrappable {
 public:
-    static PassOwnPtr<WebGLDebugShaders> create(WebGLRenderingContext*);
+    static PassRefPtr<WebGLDebugShaders> create(WebGLRenderingContext*);
     static bool supported(WebGLRenderingContext*);
     static const char* getExtensionName();