Introduce UsageTableHeader class

[ Merge of http://go/wvgerrit/23820 ]

The UsageTableHeader class is a singleton that CDM sessions will share.
A separate object will be created for each security level. The class
synchronizes access to usage table header and associated data-structures
and controls when they are read in or written out to non-secure persistent
storage. Upgrades from a fixed size usage table (supported by previous
versions of the OEMCrypto API v9-12) are handled by this class.

b/34327459

Test: Verified by unit/integration tests on angler

Change-Id: Ifc5996985e76bc260c01e55bc12aab1248389a80

libwvdrmengine/cdm/core/src/license.cpp

@@ -793,6 +793,43 @@ bool CdmLicense::IsKeyLoaded(const KeyId& key_id) {
   return loaded_keys_.find(key_id) != loaded_keys_.end();
 }
 
+bool CdmLicense::ExtractProviderSessionToken(
+    const CdmKeyResponse& license_response,
+    std::string* provider_session_token) {
+  if (license_response.empty()) {
+    LOGW("CdmLicense::ExtractProviderSessionToken: empty license response");
+    return false;
+  }
+
+  SignedMessage signed_response;
+  if (!signed_response.ParseFromString(license_response)) {
+    LOGW(
+        "CdmLicense::ExtractProviderSessionToken: unable to parse signed "
+        "license response");
+    return false;
+  }
+
+  if (signed_response.type() != SignedMessage::LICENSE) {
+    LOGW("CdmLicense::ExtractProviderSessionToken: unrecognized signed message "
+        "type: %d", signed_response.type());
+      return false;
+  }
+
+  License license;
+  if (!license.ParseFromString(signed_response.msg())) {
+    LOGE("CdmLicense::ExtractProviderSessionToken: unable to parse license "
+        "response");
+    return false;
+  }
+
+  if (license.id().has_provider_session_token()) {
+    *provider_session_token = license.id().provider_session_token();
+    return true;
+  }
+
+  return false;
+}
+
 CdmResponseType CdmLicense::HandleKeyErrorResponse(
     const SignedMessage& signed_message) {
   LicenseError license_error;