Add UMA stats for pinch-zoom behavior on Android

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 180ec300752b6dc19979842c819f1bea4948d183..09d94eb4dbe133a1f49d33f6fae854b9177bfe42 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -48784,6 +48784,24 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Viewport.DidScalePage" enum="DidScalePageEnum">
+  <owner>bokan@chromium.org</owner>
+  <summary>
+    Tracks the proportion of non-mobile optimized (i.e. no viewport tag or
+    constant width) page views that had a user initiated page scale (e.g.

[Rick Byers, 2015/09/28 18:43:58]

nit: you should explicitly include somewhere that this is tracked only on
mobile.

[bokan, 2015/10/01 20:18:31]

Done.

+    pinch-zoom, double-tap).

[Ilya Sherman, 2015/09/30 04:30:28]

Please document when this is recorded.  On page load?  On page close?  Multiple
triggers?

[bokan, 2015/10/01 20:18:31]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Viewport.MaxPageScale" units="Percent">

[bokan, 2015/09/28 13:02:09]

Is it ok that the percent value for this metric will be greater than 100? (it
maxes out at 500%)

[Ilya Sherman, 2015/09/30 04:30:28]

Yes, that's fine.  (I'd probably write units="%")

[bokan, 2015/10/01 20:18:31]

Changed this to an enum so that I can bucket the values.

+  <owner>bokan@chromium.org</owner>
+  <summary>
+    Tracks the maximum scale factor that a user has scaled zoomed to. Reported
+    only on non-mobile optimized pages (i.e. no viewport tag or constant width)
+    which have had a page scale changing gesture.

[Ilya Sherman, 2015/09/30 04:30:28]

Please document when this is recorded -- at the time of each page scaling change
gesture?

[bokan, 2015/10/01 20:18:31]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Viewport.MetaTagType" enum="MetaTagTypeEnum">
   <owner>bokan@chromium.org</owner>
   <summary>
@@ -54452,6 +54470,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="20" label="SQLite Integrity Web Data Test"/>
 </enum>
 
+<enum name="DidScalePageEnum" type="int">

[Ilya Sherman, 2015/09/30 04:30:28]

nit: Please omit the "Enum" suffix in the enum name (to match the style used
elsewhere in this file).  In fact, the typical name for this enum would be
"BooleanDidScalePage"

[bokan, 2015/10/01 20:18:31]

Done.

+  <int value="0" label="User did not change scale"/>
+  <int value="1" label="User did change scale"/>
+</enum>
+
 <enum name="DifferentPrimaryAccounts" type="int">
   <int value="0" label="Primary Accounts the same"/>
   <int value="1" label="(obsolete) Primary Accounts different"/>