Bug 672207. imglib: Time how long we spend in the decode loop. r=joe

For now this is a global counter, the eventual plan is to make this per image
format. This will be our proxy for how long we block the event loop.

--HG--
extra : rebase_source : b283fff38585825f5f46884e12508b6323e178b3

modules/libpr0n/src/RasterImage.cpp

@@ -56,6 +56,7 @@
 #include "prenv.h"
 #include "ImageLogging.h"
 #include "mozilla/TimeStamp.h"
+#include "mozilla/Telemetry.h"
 
 #include "nsPNGDecoder.h"
 #include "nsGIFDecoder2.h"
@@ -2669,7 +2670,8 @@ imgDecodeWorker::Run()
 
   // Loop control
   PRBool haveMoreData = PR_TRUE;
-  TimeStamp deadline = TimeStamp::Now() + TimeDuration::FromMilliseconds(gMaxMSBeforeYield);
+  TimeStamp start = TimeStamp::Now();
+  TimeStamp deadline = start + TimeDuration::FromMilliseconds(gMaxMSBeforeYield);
 
   // We keep decoding chunks until one of three possible events occur:
   // 1) We don't have any data left to decode
@@ -2690,6 +2692,9 @@ imgDecodeWorker::Run()
       image->mSourceData.Length() > image->mBytesDecoded;
   }
 
+  TimeDuration decodeLatency = TimeStamp::Now() - start;
+  Telemetry::Accumulate(Telemetry::IMAGE_DECODE_LATENCY, PRInt32(decodeLatency.ToMicroseconds()));
+
   // Flush invalidations _after_ we've written everything we're going to.
   // Furthermore, if this is a redecode, we don't want to do progressive
   // display at all. In that case, let Decoder::PostFrameStop() do the

toolkit/components/telemetry/TelemetryHistograms.h

@@ -68,6 +68,8 @@ HISTOGRAM(PAGE_FAULTS_HARD, 8, 64 * 1024, 13, EXPONENTIAL, "Hard page faults (si
 #endif
 HISTOGRAM(SHUTDOWN_OK, 0, 1, 2, BOOLEAN, "Did the browser start after a successful shutdown")
 
+HISTOGRAM(IMAGE_DECODE_LATENCY, 50, 5000000, 100, EXPONENTIAL, "Time spent decoding an image chunk (us)")
+
 /**
  * Networking telemetry
  */