Add UsageTableHeader metrics

[ Merge from http://go/wvgerrit/72183 ]

Adds basic metrics for the usage table header.

Bug: http://b/112919252
Test: Unit tests. Manual GPlay
Change-Id: I14d406766d8b2aba3b6e4f1a02c75eedc674b011

libwvdrmengine/cdm/core/src/crypto_session.cpp

@@ -859,6 +859,7 @@ CdmResponseType CryptoSession::Open(SecurityLevel requested_security_level) {
             }
           }
           usage_table_header_ = *header;
+          metrics_->usage_table_header_initial_size_.Record((*header)->size());
         }
       }
     }