update getFramebufferAttachmentParameter for WebGL 2

Source/core/html/canvas/WebGL2RenderingContextBase.h

Index: Source/core/html/canvas/WebGL2RenderingContextBase.h
diff --git a/Source/core/html/canvas/WebGL2RenderingContextBase.h b/Source/core/html/canvas/WebGL2RenderingContextBase.h
index 3c7987bbc47def594e6a09bb56ac269734ef3a99..5faee94126f45380b28b21484c8058bc967af092 100644
--- a/Source/core/html/canvas/WebGL2RenderingContextBase.h
+++ b/Source/core/html/canvas/WebGL2RenderingContextBase.h
@@ -167,9 +167,15 @@ public:
 
     DECLARE_VIRTUAL_TRACE();
 
+    ScriptValue getFramebufferAttachmentParameter(ScriptState*, GLenum target, GLenum attachment, GLenum pname) override;
+
 protected:
     WebGL2RenderingContextBase(HTMLCanvasElement*, PassOwnPtr<blink::WebGraphicsContext3D>, const WebGLContextAttributes& requestedAttributes);
 
+    // Helper function to validate target and the attachment combination for getFramebufferAttachmentParameters.
+    // Generate GL error and return false if parameters are illegal.
+    bool validateGetFramebufferAttachmentParameterFunc(const char* functionName, GLenum target, GLenum attachment);
+
     bool validateClearBuffer(const char* functionName, GLenum buffer, GLsizei length);
 
     ScriptValue getInt64Parameter(ScriptState*, GLenum);