Histogram to track missing and incomplete tiles

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 f307b5bc899f0cd88267310d676ddc004039399b..9bcd002571b3fce3c0b4f93d7d7cf1e6609491cc 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -24594,6 +24594,24 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="RenderPass.AppendQuadData.NumIncompleteTiles">

[Alexei Svitkine (slow), 2014/07/04 15:40:27]

There's already a "Compositing.*" namespace. Would it make sense to put these
under there instead of introducing "RenderPass.*"?

[weiliangc, 2014/07/04 21:35:53]

Done.

+  <owner>weiliangc@chromium.org.</owner>
+  <summary>
+    Keeps track of number of incomplete tiles during DrawQuad stage while
+    scrolling. This is a rough measurement of ugliness during user interaction.

[Alexei Svitkine (slow), 2014/07/04 15:40:27]

Please say explicitly when this gets sampled. i.e. something like "A sample is
recorded every time a frame is drawn while a scroll is in progress." or whatever
the correct description is. Same for the one below.

[weiliangc, 2014/07/04 21:35:53]

Done.

+    Incomplete tiles are non ideal scaled. Tracking bug 381695.
+  </summary>
+</histogram>
+
+<histogram name="RenderPass.AppendQuadData.NumMissingTiles">
+  <owner>weiliangc@chromium.org.</owner>
+  <summary>
+    Keeps track of number of missing tiles during DrawQuad stage while
+    scrolling. This is a rough measurement of ugliness during user interaction.
+    Missing tiles are checkerboard tiles. Tracking bug 381695.
+  </summary>
+</histogram>
+
 <histogram name="RenderViewContextMenu.Shown" enum="RenderViewContextMenuItem">
   <owner>vitalybuka@chromium.org</owner>
   <summary>Count of renderer view context menu items shown.</summary>