Add UMA metrics for profile switching.

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 30eb8601fe704b80fd48da67f8d28d09fcd62d2a..2162ddcc9e3d0f2db0f55ef7cdde07d0632b084a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -27857,6 +27857,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Profile.NumberofSwitches">
+  <owner>anthonyvd@chromium.org</owner>
+  <summary>
+    Counts the number of times profiles where switched in a browser session.

[Mike Lerman, 2015/01/21 20:58:03]

nit: s/where/were

Also, mention when this was logged (e.g. during shutdown).

+  </summary>
+</histogram>
+
 <histogram name="Profile.NumberOfUnusedProfiles">
   <owner>mlerman@chromium.org</owner>
   <summary>
@@ -27904,6 +27911,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Profile.ProfileSwitch" enum="ProfileOpenMethod">
+  <owner>anthonyvd@chromium.org</owner>
+  <summary>
+    Counts the number of times the user switched profiles depending on the
+    different available methods.
+  </summary>
+</histogram>
+
 <histogram name="Profile.SupervisedProfileCreateError"
     enum="GoogleServiceAuthError">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
@@ -62102,6 +62117,14 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="UserImage.ProfileDownloadTime"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="ProfileSwitch" separator=".">
+  <suffix name="ToOpenedProfile"
+      label="The profile being switched to was already opened"/>
+  <suffix name="ToUnopenedProfile"
+      label="The profile being switched to wasn't already opened"/>

[Mike Lerman, 2015/01/21 21:24:18]

Do you need to explicitly declare a no-suffix histogram? I'm not sure if one
will be created otherwise.

+  <affected-histogram name="Profile.ProfileSwitch"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="ProgressiveScan">
   <suffix name="FullScan" label="Using WPA_supplicant to scan."/>
   <suffix name="33Percent_4MinMax"