Bug 1305552 - Add telemetry to track uses of MediaKeySession.generateRequest. r=francois,gerald

This allows us to track how often EME CDMs are used, rather than just created.
The telemetry I added in bug 1304207 is reports whenever a CDM is created, but
some sites, such as the Shaka Player demo site, create CDMs without using them,
so that telemetry isn't a great measure in helping us detect when CDMs aren't
being used. Whereas the telemetry added here will report when the CDMs are used
to negotiate a license, i.e. when the CDMs are actually being used.


MozReview-Commit-ID: ExMIcIIBvS1

dom/media/eme/EMEUtils.cpp

@@ -154,4 +154,17 @@ IsClearkeyKeySystem(const nsAString& aKeySystem)
   return !CompareUTF8toUTF16(kEMEKeySystemClearkey, aKeySystem);
 }
 
+CDMType
+ToCDMTypeTelemetryEnum(const nsString& aKeySystem)
+{
+  if (!CompareUTF8toUTF16(kEMEKeySystemWidevine, aKeySystem)) {
+    return CDMType::eWidevine;
+  } else if (!CompareUTF8toUTF16(kEMEKeySystemClearkey, aKeySystem)) {
+    return CDMType::eClearKey;
+  } else if (!CompareUTF8toUTF16(kEMEKeySystemPrimetime, aKeySystem)) {
+    return CDMType::ePrimetime;
+  }
+  return CDMType::eUnknown;
+}
+
 } // namespace mozilla

dom/media/eme/EMEUtils.h

@@ -106,6 +106,16 @@ KeySystemToGMPName(const nsAString& aKeySystem);
 bool
 IsClearkeyKeySystem(const nsAString& aKeySystem);
 
+enum CDMType {
+  eClearKey = 0,
+  ePrimetime = 1,
+  eWidevine = 2,
+  eUnknown = 3
+};
+
+CDMType
+ToCDMTypeTelemetryEnum(const nsString& aKeySystem);
+
 } // namespace mozilla
 
 #endif // EME_LOG_H_

dom/media/eme/MediaKeySession.cpp

@@ -199,6 +199,9 @@ MediaKeySession::GenerateRequest(const nsAString& aInitDataType,
     return promise.forget();
   }
 
+  Telemetry::Accumulate(Telemetry::VIDEO_CDM_GENERATE_REQUEST_CALLED,
+                        ToCDMTypeTelemetryEnum(mKeySystem));
+
   // Convert initData to base64 for easier logging.
   // Note: CreateSession() Move()s the data out of the array, so we have
   // to copy it here.

dom/media/eme/MediaKeys.cpp

@@ -401,26 +401,6 @@ MediaKeys::Init(ErrorResult& aRv)
   return promise.forget();
 }
 
-enum CDMCreatedType {
-  eClearKey = 0,
-  ePrimetime = 1,
-  eWidevine = 2,
-  eUnknown = 3
-};
-
-static CDMCreatedType
-ToCDMCreatedTelemetryEnum(const nsString& aKeySystem)
-{
-  if (!CompareUTF8toUTF16(kEMEKeySystemWidevine, aKeySystem)) {
-    return CDMCreatedType::eWidevine;
-  } else if (!CompareUTF8toUTF16(kEMEKeySystemClearkey, aKeySystem)) {
-    return CDMCreatedType::eClearKey;
-  } else if (!CompareUTF8toUTF16(kEMEKeySystemPrimetime, aKeySystem)) {
-    return CDMCreatedType::ePrimetime;
-  }
-  return CDMCreatedType::eUnknown;
-}
-
 void
 MediaKeys::OnCDMCreated(PromiseId aId, const nsACString& aNodeId, const uint32_t aPluginId)
 {
@@ -440,7 +420,7 @@ MediaKeys::OnCDMCreated(PromiseId aId, const nsACString& aNodeId, const uint32_t
                                         mKeySystem,
                                         MediaKeySystemStatus::Cdm_created);
 
-  Telemetry::Accumulate(Telemetry::VIDEO_CDM_CREATED, ToCDMCreatedTelemetryEnum(mKeySystem));
+  Telemetry::Accumulate(Telemetry::VIDEO_CDM_CREATED, ToCDMTypeTelemetryEnum(mKeySystem));
 }
 
 already_AddRefed<MediaKeySession>

toolkit/components/telemetry/Histograms.json

@@ -8716,6 +8716,15 @@
     "description": "Note the type of CDM (0=ClearKey, 1=Primetime, 2=Widevine, 3=unknown) every time we successfully instantiate an EME MediaKeys object.",
     "releaseChannelCollection": "opt-out"
   },
+  "VIDEO_CDM_GENERATE_REQUEST_CALLED": {
+    "alert_emails": ["cpearce@mozilla.com"],
+    "expires_in_version": "58",
+    "bug_numbers": [1305552],
+    "kind": "enumerated",
+    "n_values": 6,
+    "description": "Note the type of CDM (0=ClearKey, 1=Primetime, 2=Widevine, 3=unknown) every time we call MediaKeySession.generateRequest().",
+    "releaseChannelCollection": "opt-out"
+  },
   "MEDIA_CODEC_USED": {
     "alert_emails": ["cpearce@mozilla.com"],
     "expires_in_version": "never",