webgl: Fix up maximum size validation.

We were checking to see if it was too big to be level 0, but we really
want to see if it's too big to be the given level.

This was the last remaining failure in texture-size-limit.html.

components/script/dom/webgl_validations/tex_image_2d.rs

@@ -163,18 +163,18 @@ impl<'a> WebGLValidator for CommonTexImage2DValidator<'a> {
             return Err(TexImageValidationError::NegativeDimension);
         }
 
+        let width = self.width as u32;
+        let height = self.height as u32;
+        let level = self.level as u32;
+
         // GL_INVALID_VALUE is generated if width or height is greater than
         // GL_MAX_TEXTURE_SIZE when target is GL_TEXTURE_2D or
         // GL_MAX_CUBE_MAP_TEXTURE_SIZE when target is not GL_TEXTURE_2D.
-        if self.width as u32 > max_size || self.height as u32 > max_size {
+        if width > max_size >> level || height > max_size >> level {
             self.context.webgl_error(InvalidValue);
             return Err(TexImageValidationError::TextureTooBig);
         }
 
-        let width = self.width as u32;
-        let height = self.height as u32;
-        let level = self.level as u32;
-
         // GL_INVALID_VALUE is generated if level is greater than zero and the
         // texture is not power of two.
         if level > 0 && (!width.is_power_of_two() || !height.is_power_of_two()) {