Fix media_cas_proxy_sdk build issue.

Add example binary for testing building the SDK after 'git clone' from our repo.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=227583629

example/wvpl_cas_proxy_environment_example.cc

@@ -0,0 +1,24 @@
+////////////////////////////////////////////////////////////////////////////////
+// Copyright 2019 Google LLC.
+//
+// This software is licensed under the terms defined in the Widevine Master
+// License Agreement. For a copy of this agreement, please contact
+// widevine-licensing@google.com.
+////////////////////////////////////////////////////////////////////////////////
+
+// Example of usage of wvpl_cas_proxy_environment.
+
+#include <iostream>
+#include <map>
+#include <string>
+
+#include "media_cas_proxy_sdk/external/common/wvpl/wvpl_cas_proxy_environment.h"
+
+int main(int argc, char **argv) {
+  std::map<std::string, std::string> config_values;
+  widevine_server::wv_pl_sdk::WvPLCASProxyEnvironment environment(
+      config_values);
+  std::cout << "Hello world!" << std::endl;
+
+  return 0;
+}

example/wvpl_cas_proxy_session_example.cc

@@ -0,0 +1,23 @@
+////////////////////////////////////////////////////////////////////////////////
+// Copyright 2019 Google LLC.
+//
+// This software is licensed under the terms defined in the Widevine Master
+// License Agreement. For a copy of this agreement, please contact
+// widevine-licensing@google.com.
+////////////////////////////////////////////////////////////////////////////////
+
+// Example of usage of wvpl_cas_proxy_session.
+
+#include <iostream>
+#include <string>
+
+#include "media_cas_proxy_sdk/external/common/wvpl/wvpl_cas_proxy_session.h"
+
+int main(int argc, char **argv) {
+  std::cout << "Session version: "
+            << widevine_server::wv_pl_sdk::WvPLCASProxySession::
+                   GetVersionString()
+            << std::endl;
+
+  return 0;
+}