Collecting UMA metrics for the UnmaskPrompt.

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 0cb8649f23eea05b2aed352551d059f8eaa5ab2b..903db44a250812ca69f922b441cb5695751ab88e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -2055,6 +2055,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Autofill.UnmaskPrompt.Events" enum="AutofillUnmaskPromptEvent">
+  <owner>waltercacau@chromium.org</owner>
+  <summary>Events tracking the usage of the unmasking prompt.</summary>

[Ilya Sherman, 2015/03/18 22:48:55]

nit: Please help users unfamiliar with this feature better understand this
metric, by briefly explaining what triggers an unmasking prompt.

[Walter Cacau, 2015/03/18 23:50:05]

Done.

+</histogram>
+
 <histogram name="Autofill.UserHappiness" enum="AutofillUserHappiness">
   <owner>isherman@chromium.org</owner>
   <summary>
@@ -44801,6 +44806,22 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="53" label="Addr. line 3, Mismatch"/>
 </enum>
 
+<enum name="AutofillUnmaskPromptEvent" type="int">
+  <int value="0" label="Shown"/>
+  <int value="1" label="Closed with no attempts"/>
+  <int value="2" label="Closed with only failed attempts (retriable)"/>
+  <int value="3" label="Closed with only failed attempts (non retriable)"/>
+  <int value="4" label="Closed with successful unmask in first attempt"/>
+  <int value="5" label="Closed with successful unmask after failed attempts"/>
+  <int value="6" label="Card saved locally"/>
+  <int value="7" label="Did opt in to local save"/>
+  <int value="8"
+      label="Did not opt in of local save (local save stayed disabled)"/>
+  <int value="9" label="Did opt out to local save"/>

[Ilya Sherman, 2015/03/18 22:48:55]

nit: "opt out to" -> "opt out of"

[Walter Cacau, 2015/03/18 23:50:05]

Done.

+  <int value="10"
+      label="Did not opt out of local save (local save stayed enabled)"/>

[Ilya Sherman, 2015/03/18 22:48:54]

Optional: Shorter labels tend to be better for readability, given the layout of
the dashboard.  For these labels in particular, I'd suggest something like:

<int value="10" label="Accepted local save">Local save stayed enabled</int>

The part that isn't the label will only be shown on hover, but that seems okay
given that it's just rephrasing the text already present in the label.

Picking another pair of long labels above, I'd suggest something like:

<int value="4" label="Closed, success w/ 0 failures">Closed with a successful
unmask on the first attempt.<int/>
<int value="5" label="Closed, success w/ 1+ failures">Closed with a successful
unmask after at least one failed attempt.<int/>

[Walter Cacau, 2015/03/18 23:50:05]

Done.

+</enum>
+
 <enum name="AutofillUserHappiness" type="int">
   <int value="0" label="Forms loaded"/>
   <int value="1" label="Submitted fillable form, autofilled all"/>