This patch merges some features that were added to TestBase in
http://go/wvgerrit/92349 in the Widevine Repo. Certain parameters to
TestBase that could have been const but weren't now are. The caller to
Initialize() can now specify additional, platform-specific help text to
be displayed after the generic help text. And some missing headers were
added to test_base.h.
The Android code does not yet take advantage of any of this, but it
could in the future.
Bug: 145013234
Test: Android Unit Tests
Change-Id: I3c54532a39641622d454256b25979ad89727d43f
1bc1bad1f0