Fix: TextView makes new layouts too frequently.

TextView#checkForRelayout was almost always called in
TextView#onRtlPropertiesChanged.
However, #onRtlPropertiesChanged just checks if re-layout
can be skipped for when the text has changed. As a result,
TextView makes new layouts too frequently in that method.

With this patch, TextView#checkForRelayout is called only
when mTextDir has actually changed.

Bug: 17971103
Change-Id: I449d8c8fd7370495cd5af9e38cada942744ca801