Significant Frame Rate Decrease in Editor UI on Monitors with G-Sync Enabled

A G-Sync enabled monitor running @100Hz will drop from 100FPS while working in the Viewport to 50FPS when scrolling through the Editor Menu window. A G-Sync enabled monitor running @60Hz will drop from 60FPS in the Viewport to 30FPS in the Editor Menu window.

This does not occur when G-Sync is not enabled.

Not a regression.

1. On a workstation with a monitor that supports G-Sync...
2. Make sure G-Sync is enabled in the Nvidia control panel
3. Make sure G-Sync is also selected in the Nvidia control panel's Manage 3D settings>Global>Monitor Technology
4. Open any project in UE 4.15
5. In Editor preferences>Miscellaneous>
6. Hover mouse anywhere inside the viewport to get a good FPS read
7. Now hover/scroll mouse over UI elements that have a tool tip, in the World Outliner for instance
   RESULT: A G-Sync enabled monitor running @100Hz will drop from 100FPS in the Viewport to 50FPS in the Editor Menu window. A G-Sync enabled monitor running @60Hz will drop from 60FPS in the Viewport to 30FPS in the Editor Menu window.
   EXPECTED: The frame rate to remain constant from the Viewport to any Editor Menu window on a monitor with G-Sync enabled.

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