Cache Max Subsample Size

(This is a merge of http://go/wvgerrit/95003.)

To reduce the number of OEMCrypto calls on the decrypt path, the maximum
subsample size will now be cached after the first call to retrieve it.

Bug: 150018606
Test: Android Unit Tests
Test: CE CDM Unit Tests
Test: ExoPlayer high-bitrate playback on OEC v15
Change-Id: I0b5d38d8a082c0a127d2a47f112b76c64085bddb

libwvdrmengine/cdm/core/include/crypto_session.h

@@ -300,7 +300,7 @@ class CryptoSession {
   CdmResponseType GetSystemIdInternal(uint32_t* system_id);
   CdmResponseType GenerateRsaSignature(const std::string& message,
                                        std::string* signature);
-  bool GetMaxSubsampleRegionSize(size_t* max);
+  size_t GetMaxSubsampleRegionSize();
 
   bool SetDestinationBufferType();
 
@@ -429,6 +429,7 @@ class CryptoSession {
   static std::atomic<uint64_t> request_id_index_source_;
 
   uint32_t api_version_;
+  size_t max_subsample_region_size_;
 
   // Stores the most recent error code returned from a call to
   // OEMCrypto_DecryptCENC.  This is used to reduce the total number of