Add UMA histogram for whether page loads are mobile optimized

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 e0170686e3ae279e158a0d2ecd54119b4fbb51e1..78bc10c4dafd51be08385e2771f5ec7aeb270bf5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -15284,6 +15284,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Navigation.IsMobileOptimized" enum="BooleanIsMobileOptimized">
+  <owner>cjhopman@chromium.org</owner>
+  <owner>nyquist@chromium.org</owner>
+  <summary>
+    Signifies whether a succesfully finished page load for the main frame
+    content width fits within the device width and/or has a fixed page scale.
+  </summary>
+</histogram>
+
 <histogram name="Navigation.MainFrameScheme" enum="NavigationScheme">
   <owner>cbentzel@chromium.org</owner>
   <owner>davidben@chromium.org</owner>
@@ -44491,6 +44500,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="1" label="Ignored"/>
 </enum>
 
+<enum name="BooleanIsMobileOptimized" type="int">
+  <int value="0" label="Not mobile optimized web page"/>
+  <int value="1" label="Mobile optimized web page"/>
+</enum>
+
 <enum name="BooleanLoaded" type="int">
   <int value="0" label="Not loaded"/>
   <int value="1" label="Loaded"/>