Allow use of cached initialization data

[ Merge of http://go/wvgerrit/41340 ]

An initial license request may actually result in a service certificate
request. Once the service certificate has been successfully handled,
an app may make a license request without needing to provide
the initialization data again. This behavior was broken in a recent
merge. Correcting the test as well.

b/72182032
Test: Ran wv unit/integration tests

Change-Id: I82401b9a3bf38140706dad859b4ae241b7ddac12

libwvdrmengine/cdm/core/src/cdm_session.cpp

@@ -372,7 +372,7 @@ CdmResponseType CdmSession::GenerateKeyRequest(
            init_data.type().c_str());
       return UNSUPPORTED_INIT_DATA;
     }
-    if (init_data.IsEmpty()) {
+    if (init_data.IsEmpty() && !license_parser_->HasInitData()) {
       LOGW("CdmSession::GenerateKeyRequest: init data absent");
       return INIT_DATA_NOT_FOUND;
     }

libwvdrmengine/cdm/test/request_license_test.cpp

@@ -1639,7 +1639,10 @@ TEST_F(WvCdmRequestLicenseTest, PrivacyModeTest) {
   std::string resp = GetKeyRequestResponse(g_license_server, g_client_auth);
   EXPECT_EQ(decryptor_.AddKey(session_id_, resp, &key_set_id_),
             wvcdm::NEED_KEY);
-  GenerateKeyRequest(g_key_id, kLicenseTypeStreaming);
+  const std::string empty_init_data;
+  // Verify cached initialization data from previous request is used when
+  // empty initialization data is passed.
+  GenerateKeyRequest(empty_init_data, kLicenseTypeStreaming);
   VerifyKeyRequestResponse(g_license_server, g_client_auth);
   decryptor_.CloseSession(session_id_);
 }