GetEnvironmentVarOrAndroidProperty will first return the given
variableName from the processes enviroment if defined. If not defined
and running on Android, will look up the corresponding property and
store it in the environment.
The framecapture code wants to see when the Android property changes so
add an uncached version of GetEnvironmentVarOrAndroidProperty that
always does the getprop command (which can be time consuming).

Bug: b/170328907
Change-Id: I0624c0646889435cb6f6eb20a6d3cceb6ae3eb48
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2520107Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>