Cherry pick 18.4 changes to udc-widevine-dev

Get the udc-widevine-dev Android branch and oemcrypto-v18 cdm branch in
sync. The commit ID for 18.4 on oemcrypto-v18 is
https://widevine-internal.git.corp.google.com/cdm/+/a2f23a2281e5e06dc2867585bdc516fa132b639.

Merged from go/wvgerrit/190151

Bug: 290252845
Test: unit tests passing on Panther device
Change-Id: I63fa3f1c784f737ca1480e5febe4f3f5a8a49948

libwvdrmengine/cdm/core/test/test_base.cpp

@@ -205,6 +205,7 @@ TestCryptoSession::TestCryptoSession(metrics::CryptoMetrics* crypto_metrics,
 
 void TestCryptoSession::MaybeInstallTestKeybox() {
   if (IsTestKeyboxNeeded()) {
+    CryptoSession::SetAllowTestKeybox(true);
     ReinitializeForTest();
     WvCdmTestBase::InstallTestRootOfTrust();
   }