media: Add UMA and trace events for CDM creation.

media/blink/cdm_session_adapter.h

Index: media/blink/cdm_session_adapter.h
diff --git a/media/blink/cdm_session_adapter.h b/media/blink/cdm_session_adapter.h
index d70e801ab9c69323d93d2bec1784488ddbf10033..13120d7dfcac22f55a0ef1c2a06fcee6dbc7a409 100644
--- a/media/blink/cdm_session_adapter.h
+++ b/media/blink/cdm_session_adapter.h
@@ -110,6 +110,7 @@ class CdmSessionAdapter : public base::RefCounted<CdmSessionAdapter> {
 
   // Callback for CreateCdm().
   void OnCdmCreated(const std::string& key_system,
+                    base::TimeTicks start_time,
                     blink::WebContentDecryptionModuleResult result,
                     scoped_ptr<MediaKeys> cdm,
                     const std::string& error_message);
@@ -134,6 +135,8 @@ class CdmSessionAdapter : public base::RefCounted<CdmSessionAdapter> {
   WebContentDecryptionModuleSessionImpl* GetSession(
       const std::string& session_id);
 
+  void ReportCdmCreationTimeUMA(base::TimeDelta cdm_creation_time);

[ddorwin, 2015/07/20 21:35:21]

static? At least const?

[ddorwin, 2015/07/20 21:35:21]

nit: "Time" makes it sound like, for example, the UTC time rather than duration.
See also the UMA naming comment.

Naming the variable "duration" would be at least an improvement even if the
function is harder to name.

Also, we probably don't need the "cdm_creation_" part as it's redundant.

[xhwang, 2015/07/20 22:11:57]

Can't be static since we need GetKeySystemUMAPrefix().
Done.

[xhwang, 2015/07/20 22:11:57]

See the reply about the UMA naming.
Done.

+
   scoped_ptr<MediaKeys> cdm_;
 
   SessionMap sessions_;
@@ -141,6 +144,10 @@ class CdmSessionAdapter : public base::RefCounted<CdmSessionAdapter> {
   std::string key_system_;
   std::string key_system_uma_prefix_;
 
+  // A unique ID to trace CdmSessionAdapter::CreateCdm() call and the matching
+  // OnCdmCreated() call.
+  uint32 trace_id_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<CdmSessionAdapter> weak_ptr_factory_;