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/include/cdm_engine.h

@@ -26,6 +26,7 @@
 namespace wvcdm {
 
 class CdmClientPropertySet;
+class CdmEngineFactory;
 class CdmSession;
 class CryptoEngine;
 class UsagePropertySet;
@@ -37,7 +38,6 @@ typedef std::map<CdmKeySetId,
 
 class CdmEngine {
  public:
-  CdmEngine(FileSystem* file_system, const std::string& spoid = EMPTY_SPOID);
   virtual ~CdmEngine();
 
   // Session related methods
@@ -316,10 +316,37 @@ class CdmEngine {
   // dead lock.
   virtual void OnTimerEvent();
 
-  virtual metrics::EngineMetrics* GetMetrics() { return &metrics_; }
+  // Fills the |engine_metrics| parameter with the current snapshot of metrics
+  // data. Returns true if the metrics data is populated, false otherwise.
+  // |engine_metrics| is owned by the caller and must not be null.
+  // The CdmEngine implementation is a placeholder. Just return false.
+  virtual bool GetMetricsSnapshot(
+      __attribute__((unused)) drm_metrics::WvCdmMetrics *metrics) {
+    return false;
+  }
 
   virtual CdmResponseType ValidateServiceCertificate(const std::string& cert);
 
+  // Setter and getter for the |app_package_name| identifier for this instance
+  // of the CdmEngine. This is used to identify the package name.
+  virtual void SetAppPackageName(const std::string& app_package_name) {
+    app_package_name_ = app_package_name;
+  }
+  virtual const std::string& GetAppPackageName() {
+    return app_package_name_;
+  }
+
+ protected:
+  friend class CdmEngineFactory;
+  friend class WvCdmEnginePreProvTest;
+  friend class WvCdmTestBase;
+  friend class WvGenericOperationsTest;
+  friend class TestLicenseHolder;
+
+  CdmEngine(FileSystem* file_system,
+            std::shared_ptr<metrics::EngineMetrics> metrics,
+            const std::string& spoid = EMPTY_SPOID);
+
  private:
   // private methods
   CdmResponseType OpenSession(
@@ -348,7 +375,8 @@ class CdmEngine {
    * ensure that all data has been properly recorded in the group before
    * it is published.
    */
-  metrics::EngineMetrics metrics_;
+  std::shared_ptr<metrics::EngineMetrics> metrics_;
+  std::string app_package_name_;
 
   CdmSessionMap session_map_;
   CdmReleaseKeySetMap release_key_sets_;