Fix gcc-4_9 warning

Fix a warning in gcc-4.9:
In file included from
vendor/widevine/libwvdrmengine/cdm/core/src/max_res_engine.cpp:3:0:
vendor/widevine/libwvdrmengine/cdm/core/include/max_res_engine.h:56:9:
error: 'class wvcdm::MaxResEngine::KeyStatus' is private
   class KeyStatus {
         ^
vendor/widevine/libwvdrmengine/cdm/core/src/max_res_engine.cpp:10:53:
error: within this context
 typedef std::map<wvcdm::KeyId,
wvcdm::MaxResEngine::KeyStatus*>::const_iterator

Change-Id: Ic92676d09c84582de18091a91ea8742a6faf05e7

libwvdrmengine/cdm/core/include/max_res_engine.h

@@ -78,6 +78,8 @@ class MaxResEngine {
     ConstraintList constraints_;
   };
 
+  typedef std::map<wvcdm::KeyId, KeyStatus*>::const_iterator KeyIterator;
+
   void Init(CryptoSession* crypto_session, Clock* clock);
 
   void DeleteAllKeys();

libwvdrmengine/cdm/core/src/max_res_engine.cpp

@@ -7,9 +7,6 @@
 
 namespace {
 
-typedef std::map<wvcdm::KeyId, wvcdm::MaxResEngine::KeyStatus*>::const_iterator
-    KeyIterator;
-
 const int64_t kHdcpCheckInterval = 10;
 const uint32_t kNoResolution = 0;