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 bbcc8de66f29ef2be8bd9d36b89814b928a6cd1d..a3d6a797649e79ce964b6cc3a51ea2982fb4e888 100644
--- a/Source/core/html/canvas/WebGL2RenderingContextBase.h
+++ b/Source/core/html/canvas/WebGL2RenderingContextBase.h
@@ -161,11 +161,17 @@ public:
 
     DECLARE_VIRTUAL_TRACE();
 
+    ScriptValue getFramebufferAttachmentParameter(ScriptState*, GLenum target, GLenum attachment, GLenum pname) override;
+
 protected:
     WebGL2RenderingContextBase(HTMLCanvasElement*, PassOwnPtr<blink::WebGraphicsContext3D>, const WebGLContextAttributes& requestedAttributes);
 
     bool validateClearBuffer(const char* functionName, GLenum buffer, GLsizei length);
 
+    // Helper function to validate target and the attachment combination for getFramebufferAttachmentParameters.
+    // Generate GL error and return false if parameters are illegal.
+    bool validateGetFramebufferAttachmentParameters(const char* functionName, GLenum target, GLenum attachment);
+
     /* WebGLRenderingContextBase overrides */
     bool validateCapability(const char* functionName, GLenum) override;
     bool validateAndUpdateBufferBindTarget(const char* functionName, GLenum, WebGLBuffer*) override;