Generate a unique license request ID

The request ID was set to a fixed value, which caused license requests
to be rejected by the YT server with TOO_MANY_STREAMS_PER_VIDEO

The request ID is now a combination of a randomly generated value and
a rolling index. This is based off a fix by gmorgan@ on the eureka
branch #98fa6e5e.

Merge of https://widevine-internal-review.googlesource.com/#/c/8496/
from the widevine cdm repo.

b/12018697

Change-Id: I6c05fea885d46aea53a07235c3e5ac65a6971eaf

libwvdrmengine/cdm/core/include/crypto_session.h

@@ -94,6 +94,9 @@ class CryptoSession {
 
   KeyId key_id_;
 
+  uint64_t request_id_base_;
+  static uint64_t request_id_index_;
+
   CORE_DISALLOW_COPY_AND_ASSIGN(CryptoSession);
 };