MacViews: Implement BridgedNativeWidget::PrepareForLayerBoundsChange().

Just removed NOTIMPLEMENTED from
BridgedNativeWidget::PrepareForLayerBoundsChange() function.

BUG=454698

Review URL: https://codereview.chromium.org/1627193004

Cr-Commit-Position: refs/heads/master@{#371763}

ui/views/cocoa/bridged_native_widget.mm

@@ -918,7 +918,6 @@ void BridgedNativeWidget::OnDeviceScaleFactorChanged(
 }
 
 base::Closure BridgedNativeWidget::PrepareForLayerBoundsChange() {
-  NOTIMPLEMENTED();
   return base::Closure();
 }