Add xml entries for Networks.* UMA histograms

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 83839e40d228618760d0f2a79b0bf537b2462709..047d1cfbc05ccb595485e6676d28575fdaff919b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -20753,6 +20753,30 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Networks.RememberedShared">
+  <owner>stevenjb@chromium.org</owner>
+  <summary>
+    Number of shared remembered (preferred) networks on Chrome OS. Updated any
+    time the network list changes.

[jar (doing other things), 2014/10/20 22:08:42]

Thanks... that makes it clearer... but does leave me wondering what this stat
will mean?

I suspect that if a ton of users have a dozen networks listed, but never change
them, then you'll get no samples from them.

Similarly, a "silly" user that wanted to "keep the list short and clean" and
constantly deletes unused access points, will provide <sadly> the bulk of the
samples!?!

How do you plan to use this stat? What do you expect it to show, given the
biases? how do you plan on distinguishing the sources of bias?

Have you considered alternatively, or additional doing something like:

a) A histogram that samples this no more than once per day?  This would get
"more" samples from folks that use the browser "every day."

b) A histogram that samples this after N hours of running the browser? This gets
extra samples from heavy users (or at least users that leave their CrOS or
browser "on").

c) A histogram that samples this after P pages have been loaded (use page load
metrics to drive).  This biases samples towards "heavy users" or "proportional
to usage."

+  </summary>
+</histogram>
+
+<histogram name="Networks.RememberedUnshared">
+  <owner>stevenjb@chromium.org</owner>
+  <summary>
+    Number of private remembered (preferred) networks on Chrome OS. Updated any
+    time the network list changes.
+  </summary>
+</histogram>
+
+<histogram name="Networks.Visible">
+  <owner>stevenjb@chromium.org</owner>
+  <summary>
+    Number of visible (in-range) networks on Chrome OS. Updated any time the
+    network list changes.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.ActionAndroid" enum="NewTabPageActionAndroid">
   <owner>newt@chromium.org</owner>
   <summary>