Record the TaskLatency Histogram in Microseconds Instead of Milliseconds

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index d476b29069e83525241378e66c58b9d231e3693f..84e36f6178c40ae0291a54cba8cc55889bab7248 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -74301,6 +74301,19 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="TaskScheduler.TaskLatency" units="ms">
+  <obsolete>
+    Deprecated 4/2017. Units changed from milliseconds to microseconds.
+  </obsolete>
+  <owner>fdoray@chromium.org</owner>
+  <owner>gab@chromium.org</owner>
+  <owner>robliao@chromium.org</owner>
+  <summary>
+    Time elapsed between when a task is posted and when it starts to run.
+    Recorded for each task that runs inside the TaskScheduler.
+  </summary>
+</histogram>
+
+<histogram name="TaskScheduler.TaskLatencyMicroseconds" units="microseconds">

[Ilya Sherman, 2017/04/27 21:24:01]

nit: Mebbe mark as base="true" -- there's no data emitted to this histogram
directly, right?

[robliao, 2017/04/27 21:42:22]

Yep. Done.

   <owner>fdoray@chromium.org</owner>
   <owner>gab@chromium.org</owner>
   <owner>robliao@chromium.org</owner>
@@ -127425,10 +127438,27 @@ from previous Chrome versions.
   <suffix name="MayBlock"
       label="Applies to tasks posted with MayBlock() or
              WithBaseSyncPrimitives()."/>
-  <affected-histogram name="TaskScheduler.TaskLatency.BackgroundTaskPriority"/>
+  <affected-histogram name="TaskScheduler.TaskLatency.BackgroundTaskPriority">
+    <obsolete>
+      Deprecated 4/2017. Units changed from milliseconds to microseconds.
+    </obsolete>
+  </affected-histogram>
+  <affected-histogram name="TaskScheduler.TaskLatency.UserBlockingTaskPriority">
+    <obsolete>
+      Deprecated 4/2017. Units changed from milliseconds to microseconds.
+    </obsolete>
+  </affected-histogram>
+  <affected-histogram name="TaskScheduler.TaskLatency.UserVisibleTaskPriority">
+    <obsolete>
+      Deprecated 4/2017. Units changed from milliseconds to microseconds.
+    </obsolete>
+  </affected-histogram>
   <affected-histogram
-      name="TaskScheduler.TaskLatency.UserBlockingTaskPriority"/>
-  <affected-histogram name="TaskScheduler.TaskLatency.UserVisibleTaskPriority"/>
+      name="TaskScheduler.TaskLatencyMicroseconds.BackgroundTaskPriority"/>
+  <affected-histogram
+      name="TaskScheduler.TaskLatencyMicroseconds.UserBlockingTaskPriority"/>
+  <affected-histogram
+      name="TaskScheduler.TaskLatencyMicroseconds.UserVisibleTaskPriority"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="TaskSchedulerTaskPriority" separator=".">
@@ -127438,7 +127468,11 @@ from previous Chrome versions.
       label="Applies to tasks posted with a USER_VISIBLE priority."/>
   <suffix name="UserBlockingTaskPriority"
       label="Applies to tasks posted with a USER_BLOCKING priority."/>
-  <affected-histogram name="TaskScheduler.TaskLatency"/>
+  <affected-histogram name="TaskScheduler.TaskLatency">
+    <obsolete>
+      Deprecated 4/2017. Units changed from milliseconds to microseconds.
+    </obsolete>

[Ilya Sherman, 2017/04/27 21:24:01]

nit: I think it's fine to just mark the base histogram as obsolete; it should
bubble up to the rest.

[robliao, 2017/04/27 21:42:22]

Done.

+  </affected-histogram>
   <affected-histogram name="TaskScheduler.TaskLatency.BackgroundFileIOPool">
     <obsolete>
       Deprecated 12/2016. Pool name removed from task latency histogram name.
@@ -127459,6 +127493,7 @@ from previous Chrome versions.
       Deprecated 12/2016. Pool name removed from task latency histogram name.
     </obsolete>
   </affected-histogram>
+  <affected-histogram name="TaskScheduler.TaskLatencyMicroseconds"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="TaskSchedulerWorkerPool" separator=".">