Add a triggered profile reset mechanism.

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 aa44430b34ea4becc99aa7f430e441924ec69b2f..e25dc98e41ead459e7157d620f83ffc73907722f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -35260,6 +35260,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Total size of the profile data (excluding sub-folders).</summary>
 </histogram>
 
+<histogram name="Profile.TriggeredReset" enum="BooleanHit">

[Alexei Svitkine (slow), 2015/09/14 17:05:43]

Nit: Add a custom enum for this - e.g. BooleanReset.

[robertshield, 2015/09/21 04:16:23]

Ok, done. Curious: what is the benefit of having every new histogram get its own
enum? 400 lines of this file are devoted to boolean-type enums with the main
difference being labels that don't seem to provide much additional clarity. 

+  <owner>robertshield@chromium.org</owner>
+  <summary>Indicates whether a profile was reset via a reset trigger.</summary>

[Alexei Svitkine (slow), 2015/09/14 17:05:43]

Mention when it's recorded.

[robertshield, 2015/09/21 04:16:23]

Done.

+</histogram>
+
 <histogram name="Profile.Update" enum="ProfileType">
   <owner>rlp@chromium.org</owner>
   <summary>Times a profile name and/or avatar was updated.</summary>