Add a metric decorator around cdm engine

[ Merge from http://go/wvgerrit/69105 ]

This adds a metric collecting decorator class around cdm engine. This
implementation uses a templated decorator. The decorator enables:

1) Wrapping the CDM Engine methods to capture timing and error
information.
2) Allows use of a mock CDM Engine for testing.

Test: Unit tests. GPlay manual testing and GTS tests.
BUG: http://b/64724336
Change-Id: I5e4a0f552974fab1939bc7ab02719a1f5849cf3f

libwvdrmengine/cdm/core/test/test_base.cpp

@@ -27,6 +27,8 @@
 #include "test_printers.h"
 #include "url_request.h"
 
+using wvcdm::metrics::EngineMetrics;
+
 namespace wvcdm {
 namespace {
 void show_menu(char* prog_name) {
@@ -262,8 +264,10 @@ void WvCdmTestBase::Provision() {
 
   CdmSessionId session_id;
   FileSystem file_system;
+
   // TODO(fredgc): provision for different SPOIDs.
-  CdmEngine cdm_engine(&file_system);
+  CdmEngine cdm_engine(&file_system,
+                       std::shared_ptr<EngineMetrics>(new EngineMetrics));
 
   CdmResponseType result = cdm_engine.GetProvisioningRequest(
       cert_type, cert_authority, config_.provisioning_service_certificate(),
@@ -325,7 +329,8 @@ void WvCdmTestBase::Provision() {
 void WvCdmTestBase::EnsureProvisioned() {
   CdmSessionId session_id;
   FileSystem file_system;
-  CdmEngine cdm_engine(&file_system);
+  CdmEngine cdm_engine(&file_system,
+                       std::shared_ptr<EngineMetrics>(new EngineMetrics));
   CdmResponseType status =
       cdm_engine.OpenSession(config_.key_system(), NULL, NULL, &session_id);
   if (status == NEED_PROVISIONING) {