Bug 1369538 - Telemetry MEDIACACHESTREAM_LENGTH_KB - r=cpearce,francois

Capture each media stream's length (as provided, otherwise as actually
downloaded), to gauge whether keeping media in memory would have a significant
impact.

MozReview-Commit-ID: 4yUQrbgLcGG

--HG--
extra : rebase_source : bed0ea1d58f864463926478b0f8ea59e7084c4af

dom/media/MediaCache.cpp

@@ -1966,6 +1966,15 @@ MediaCacheStream::~MediaCacheStream()
     gMediaCache->ReleaseStream(this);
     MediaCache::MaybeShutdown();
   }
+
+  uint32_t lengthKb = uint32_t(
+    std::min(std::max(mStreamLength, int64_t(0)) / 1024, int64_t(UINT32_MAX)));
+  LOG("MediaCacheStream::~MediaCacheStream(this=%p) "
+      "MEDIACACHESTREAM_LENGTH_KB=%" PRIu32,
+      this,
+      lengthKb);
+  Telemetry::Accumulate(Telemetry::HistogramID::MEDIACACHESTREAM_LENGTH_KB,
+                        lengthKb);
 }
 
 void

toolkit/components/telemetry/Histograms.json

@@ -8398,6 +8398,16 @@
     "n_values": 32,
     "description": "Maximum number of owners for each MediaCache block. Recorded at every MediaCache destruction, i.e., whenever there is no more media data to be downloaded or kept for playback."
   },
+  "MEDIACACHESTREAM_LENGTH_KB": {
+    "record_in_processes": ["main", "content"],
+    "alert_emails": ["gsquelart@mozilla.com"],
+    "bug_numbers": [1369538],
+    "expires_in_version": "60",
+    "kind": "linear",
+    "high": 520000,
+    "n_buckets": 66,
+    "description": "MediaCacheStream stream length size in KB; Either known size from the HTTP header if available, or otherwise the size actually downloaded. Recorded at every MediaCacheStream destruction."
+  },
   "VIDEO_MFT_OUTPUT_NULL_SAMPLES": {
     "record_in_processes": ["main", "content"],
     "alert_emails": ["cpearce@mozilla.com"],