Reduce Duplication in CryptoPlugin

(This is a merge of go/wvgerrit/22898)

This change moves some code - that was nearly identical between the
clear subsample and encrypted subsample paths - into a common helper
method.

Bug: 31381719
Test: libwvdrmmediacrypto_test
Change-Id: I64d3e03b3953cddd1cc0d370ba66fc634dfb1dd8

libwvdrmengine/mediacrypto/include/WVCryptoPlugin.h

@@ -45,6 +45,9 @@ class WVCryptoPlugin : public android::CryptoPlugin {
   wvcdm::CdmSessionId mSessionId;
 
   wvcdm::CdmSessionId configureTestMode(const void* data, size_t size);
+  android::status_t attemptDecrypt(
+      const wvcdm::CdmDecryptionParameters& params,
+      bool haveEncryptedSubsamples, android::AString* errorDetailMsg);
   static wvcdm::CdmResponseType countEncryptedBlocksInPatternedRange(
       size_t range, const Pattern& pattern, uint64_t* result);
   static void incrementIV(uint64_t increaseBy, std::vector<uint8_t>* ivPtr);