Use standardized and extendable accelerometer update type.
Updates the type used when delivering accelerometer updates in ash to:
- support a variable number of accelerometers
- be measured in m/s^2
- use axes consistent with the web device motion API.
BUG=380831
TEST=MaximizeModeController unit tests still pass.
TEST=Run on a touchview device and verify that entering / exiting touchview as well as screen rotation still works.
Review URL: https://codereview.chromium.org/
500613003
Cr-Commit-Position: refs/heads/master@{#292968}