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
a2f23a2281e5e06dc2867585bdc516fa132b6396.

Merged from go/wvgerrit/190151

Bug: 290252845
Test: WVTS tests are running and passing
Change-Id: I457332e7ca70a5b5169345e1279b3eb9f18413b6

libwvdrmengine/oemcrypto/test/fuzz_tests/oemcrypto_generate_signature.cc

@@ -0,0 +1,37 @@
+#include "properties.h"
+#include "oemcrypto_session_tests_helper.h"
+
+using namespace wvoec;
+
+static bool is_init = false;
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  SessionUtil session_helper;
+  if (!is_init) {
+    wvoec::global_features.Initialize();
+    wvoec::global_features.RestrictFilter("*");
+    wvutil::Properties::Init();
+    is_init = true;
+  }
+
+  OEMCrypto_Initialize();
+  OEMCrypto_EnterTestMode();
+  session_helper.EnsureTestROT();
+
+  Session s;
+  s.open();
+  s.GenerateDerivedKeysFromKeybox(session_helper.keybox_);
+
+  static const uint32_t SignatureBufferMaxLength = size;
+  vector<uint8_t> signature(SignatureBufferMaxLength);
+  size_t signature_length = signature.size();
+
+  OEMCryptoResult sts;
+  sts = OEMCrypto_GenerateSignature(s.session_id(), data, size,
+                                    &signature[0], &signature_length);
+
+  s.close();
+  OEMCrypto_Terminate();
+
+  return 0;
+}