Kill dummy highlight component now that Chrome 35 fixes render artifact

Previously, removing the last highlight caused rendering artifacts.
Chrome 35 no longer exhibits this problem so we can remove this
workaround.
Use requestAnimationFrame to batch updates in Chrome 35

In Chrome 31, setImmediate was yielding better behavior. But now Chrome
35 seems to behave more smoothly when we use requestAnimationFrame, and
the delay for keystrokes is non-existent.
Stop polling when an update is pending