Setup test ROT + log empty root key in ref

Bug: b/117897682
Test: unit tests

Merge of http://go/wvgerrit/65223

Gtest setup does not call the base class' setup if it's defined in the
derived class. As a result, the WvCdmEngineTests were not installing the
test root of trusts in the OEMCrypto, which leads to segfaults when
using a key derived from the root of trust when a real root of trust
doesn't exist. The test class' setup is changed to use its base class'
methods, and logging is added to handle empty derived keys.

Change-Id: Ia574c4ade48206d771d6079fb3b67ccd7653428c

libwvdrmengine/oemcrypto/ref/src/oemcrypto_old_usage_table_ref.cpp

@@ -95,6 +95,11 @@ OldUsageTable::OldUsageTable(CryptoEngine *ce) {
   // This should be encrypted and signed with a device specific key.
   // For the reference implementation, I'm just going to use the keybox key.
   const std::vector<uint8_t> &key = ce_->DeviceRootKey();
+  if (key.empty()) {
+    LOGE("OldUsageTable: DeviceRootKey is unexpectedly empty.");
+    table_.clear();
+    return;
+  }
 
   uint8_t computed_signature[SHA256_DIGEST_LENGTH];
   unsigned int sig_length = sizeof(computed_signature);