This patch adds a new interface that partners must provide to
Cdm::initialize(), ILogger. ILogger replaces stderr as the sink to which
logging messages are sent. For partners that still want to log to
stderr, a reference implementation that logs to stderr is provided.
As a side-effect of this, many test-related source files had to be
updated to thread the new parameter to Cdm::initialize() through them.
This also necessitated adding a new variant of FormatString() that can
be called with a va_list directly so it can be called from other
functions that take varargs.
Bug: 201446862
Merged from https://widevine-internal-review.googlesource.com/177270
Change-Id: Ie31a10162773883b337f3a6144cf180a2b100139
c232299f78