SF: Don't bump to PERFORMANCE refresh rate with infrequent updates

Testing scenario:
1. Set brightness around 50%-55%, set dark theme.
2. Open Chrome.
3. Click search bar.
4. Can see the cursor show up.
Notice the flickering of the screen.

Explanation:
Kernel idle timer detects inactivity after 100ms, and turns the refresh rate to 60Hz.
When a cursor update happens (every 500ms), SF receives a new frame, notifies kernel,
the refresh rate bumps to 90Hz. After 100ms the kernel again decreases the refresh rate to 60Hz.

Desired goals:
Stop the flickering (eg. changing between 60-90Hz too often).
Continue having low battery impact.

Solution in this AG:
Add logic to SF to detect infrequent updates (for all layers). Description of the algorithm:
1) Store the timestamp of the last two buffers.
2) If the first buffer is older than 250 ms, detect inactivity, go into DEFAULT refresh rate.
3) EXIT: on touch event, layer requests 2 or more frames in less than 250ms.
NOTE: if the application is explicitly requesting 90Hz, SF does not override that. Idle kernel
still kicks in, and the flickering happens.

tested on Chrome v74 Beta, and messaging app.

Test: manual, b/135009095
Bug: 135718869
Change-Id: I72d8cd48b3ec900989afcf0fab1cdc3046b87274
(cherry picked from commit ad083c40)
Merged-In: I72d8cd48b3ec900989afcf0fab1cdc3046b87274