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..314439a787a6df982f81a1c661b735d48b2e627b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -10982,6 +10982,32 @@ 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). Emitted
+    shortly after startup when constructing the initial UMA log.

[Mark P, 2015/03/18 18:45:46]

Please put this last sentence in the other histograms as well.

[Dan Beam, 2015/03/18 19:19:42]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Hardware.Drive.HasSeekPenalty_Success" enum="BooleanSuccess">
+  <owner>dbeam@chromium.org</owner>
+  <summary>
+    Whether it was possible to determine if a drive has a seek penalty. This can
+    fail for various reasons (device drivers don't offer this information, the
+    drive is still mounting, lack of access, etc.).
+  </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.
+    Recorded every time a drive is queried as to whether it has a seek penalty
+    (currently twice shortly after startup).

[Mark P, 2015/03/18 18:45:46]

Is this last point (recorded twice) true for the other histograms as well?  If
so, say so on those places.  Not everyone will read all these three descriptions
at the same time.  They all read all the relevant information in each of them.

[Dan Beam, 2015/03/18 19:19:42]

Done.

+  </summary>
+</histogram>
+
 <histogram name="HIDDetection.OOBEDevicesDetectedOnContinuePressed"
     enum="HIDContinueScenarioType">
   <owner>merkulova@chromium.org</owner>
@@ -45103,6 +45129,11 @@ 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"/>