[TIMOB-23802] Android N: Expose Sustained Performance API for Nexus devices

{quote} Performance can fluctuate dramatically for long-running apps, because the system throttles system-on-chip engines as device components reach their temperature limits. This fluctuation presents a moving target for app developers creating high-performance, long-running apps. To address these limitations, Android 7.0 includes support for sustained performance mode, enabling OEMs to provide hints about device-performance capabilities for long-running apps. App developers can use these hints to tune apps for a predictable, consistent level of device performance over long periods of time. App developers can try out this new API in Android 7.0 on Nexus 6P devices only. To use this feature, set the sustained performance window flag for the window you want to run in sustained performance mode. Set this flag using the Window.setSustainedPerformanceMode() method. The system automatically disables this mode when the window is no longer in focus. {quote}