Record histogram of reason for quads not being put in an overlay.

tools/metrics/histograms/enums.xml

Index: tools/metrics/histograms/enums.xml
diff --git a/tools/metrics/histograms/enums.xml b/tools/metrics/histograms/enums.xml
index f09bdb34d9ca857edd35d8fc5f3cc69063b3716c..00024349f5c792df6c3357bd5b03e69c421143ba 100644
--- a/tools/metrics/histograms/enums.xml
+++ b/tools/metrics/histograms/enums.xml
@@ -6875,6 +6875,15 @@ uploading your change for review.  These are checked by presubmit scripts.
   <int value="40" label="LargeIconService"/>
 </enum>
 
+<enum name="DCLayerResult" type="int">
+  <int value="0" label="Success"/>
+  <int value="1" label="Failed unsupported quad"/>
+  <int value="2" label="Failed quad blend mode"/>
+  <int value="3" label="Failed texture not candidate"/>
+  <int value="4" label="Failed occluded"/>
+  <int value="5" label="Failed complex transform"/>
+</enum>
+
 <enum name="DeclarativeAPIFunctionType" type="int">
   <int value="0" label="kDeclarativeContentAddRules"/>
   <int value="1" label="kDeclarativeContentRemoveRules"/>