Bug 811461. Switch IMAGE_DECODE_LATENCY to microseconds. r=taras

Currently this is recording in ms when we expect all of the values to be <5ms
I believe this was just a typo.

--HG--
extra : rebase_source : ed71dc9bd7dc9ef0903e2e84152b44ba13d97adf

image/src/RasterImage.cpp

@@ -3393,8 +3393,8 @@ RasterImage::DecodeWorker::Run()
     EnsurePendingInEventLoop();
   }
 
-  Telemetry::Accumulate(Telemetry::IMAGE_DECODE_LATENCY,
-                        uint32_t((TimeStamp::Now() - eventStart).ToMilliseconds()));
+  Telemetry::Accumulate(Telemetry::IMAGE_DECODE_LATENCY_US,
+                        uint32_t((TimeStamp::Now() - eventStart).ToMicroseconds()));
 
   return NS_OK;
 }

toolkit/components/telemetry/Histograms.json

@@ -457,7 +457,7 @@
     "kind": "boolean",
     "description": "Did the browser start after a successful shutdown"
   },
-  "IMAGE_DECODE_LATENCY": {
+  "IMAGE_DECODE_LATENCY_US": {
     "kind": "exponential",
     "low": 50,
     "high": "5000000",