metrics: log whether drives have seek penalties (and whether this was determined successfully).

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 45ab30df9b7a9c0adbc0687ca07a10bb6f9da82f..10efcc6d933c557f2ad44f9febb28c77c23c62a8 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -10982,6 +10982,28 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Hardware.Drive.HasSeekPenalty" enum="BooleanHasSeekPenalty">
+  <owner>dbeam@chromium.org</owner>
+  <summary>
+    Whether a drive has a seek penalty (i.e. is a spinning disk).

[Mark P, 2015/03/18 18:17:43]

All histograms should mention when they're recorded.  e.g., Emitted shortly
after startup when constructing the initial UMA log.
(I think that's right; correct me if I'm wrong.)

[Dan Beam, 2015/03/18 18:33:51]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Hardware.Drive.HasSeekPenalty_Success" enum="BooleanSuccess">
+  <owner>dbeam@chromium.org</owner>
+  <summary>
+    Whether it was possible to determine whether a drive has a seek penalty.
+    This can fail when drivers don't offer this information.

[Mark P, 2015/03/18 18:17:43]

drivers?
drives?

[Dan Beam, 2015/03/18 18:33:51]

actually meant drivers but technically both are correct (the driver tells the
system the capabilities of the drive).

see updated comment

+  </summary>
+</histogram>
+
+<histogram name="Hardware.Drive.HasSeekPenalty_Time" units="milliseconds">
+  <owner>dbeam@chromium.org</owner>
+  <summary>
+    The amount of time it takes to determine whether a drive has a seek penalty.
+  </summary>
+</histogram>
+
 <histogram name="HIDDetection.OOBEDevicesDetectedOnContinuePressed"
     enum="HIDContinueScenarioType">
   <owner>merkulova@chromium.org</owner>
@@ -45103,6 +45125,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="1" label="Has distilled data"/>
 </enum>
 
+<enum name="BooleanHasSeekPenalty" type="int">
+  <int value="0" label="Has no seek penalty (e.g. is flash memory)"/>
+  <int value="1" label="Has seek penalty (e.g. spinning disk)"/>
+</enum>
+
 <enum name="BooleanHit" type="int">
   <int value="0" label="Not_reached"/>
   <int value="1" label="Hit"/>