Fix math errors causing black screen. DO NOT MERGE

Turning off animations in the Developer options creates a ValueAnimator
duration scale of 0. This is used as the denominator in RampAnimator
which, if the numerator is also 0, sets mAnimatedValue to NaN. Rounding
NaN to the nearest int produces 0 which is then assigned to
mScreenBrightness in DisplayPowerState.

A copy mistake which assigned mTransitionAnimationScale as the default
value for mAnimatorDurationScale in WindowManagerService is also
fixed here.

Bug 7515609 fixed.

Change-Id: I39f8d0a7abdd5a1fe70d757fe95fbddaf7a0ed51