Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/WebGLExtension.h

Index: Source/core/html/canvas/WebGLExtension.h
diff --git a/Source/core/html/canvas/WebGLExtension.h b/Source/core/html/canvas/WebGLExtension.h
index 6cef3af7c853dab86f5641e48b096c2ca9469e44..8fe34903d91d4092bcdf7627eb74f3dd0a2ac82d 100644
--- a/Source/core/html/canvas/WebGLExtension.h
+++ b/Source/core/html/canvas/WebGLExtension.h
@@ -59,10 +59,30 @@ public:
 
     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