account for pixel scale when checking against existing buffer storage size (#4103)

shell/platform/darwin/ios/ios_gl_context.mm

@@ -163,9 +163,10 @@ bool IOSGLContext::PresentRenderBuffer() const {
 
 bool IOSGLContext::UpdateStorageSizeIfNecessary() {
   const CGSize layer_size = [layer_.get() bounds].size;
+  const CGFloat contents_scale = layer_.get().contentsScale;
 
-  const GLint size_width = layer_size.width;
-  const GLint size_height = layer_size.height;
+  const GLint size_width = layer_size.width * contents_scale;
+  const GLint size_height = layer_size.height * contents_scale;
 
   if (size_width == storage_size_width_ && size_height == storage_size_height_) {
     // Nothing to since the stoage size is already consistent with the layer.