[Latest Macbook Pro][Metal] blinks severely

• This bug causes the screen to flicker randomly, even in simple, blank third person project templates. Even the basic starter content, the main editor area is blinking all the time if the user chooses Metal API on Macbook Pro.

However if the user forces XCode use opengl to build UE4.15, everything is fine except the warning of deprecation of OpenGL on Mac.

The following link shows the effect: [Link Removed]

Cannot reproduce on 2013 Macbook pro (See specs below)

User's repro steps:

1. Open UE 4.15 on Latest 13inch Macbook Pro with Retina Screen
2. Start any basic starter template using Metal API
   RESULT: "Black screen tearing (described as "blinking") occurs
   EXPECTED: No screen tearing or artifacts to be present

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