Add UMA for CopylessPaste cache

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 5c644c89bdedc7494b375c9e31d5ee583f8da387..0240f0b7040d45da1b424463cda3501bf3072ba8 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9199,6 +9199,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>For each cookie added to the store, record it's type(s).</summary>
 </histogram>
 
+<histogram name="CopylessPaste.CacheHit" enum="CopylessCacheHit">
+  <owner>wychen@chromium.org</owner>
+  <summary>
+    The cache hit status of metadata extraction for AppIndexing.
+  </summary>
+</histogram>
+
 <histogram name="CopylessPaste.ExtractionFailedUs" units="microseconds">
   <owner>wychen@chromium.org</owner>
   <summary>
@@ -87783,6 +87790,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="7" label="First-Party-Only, HttpOnly, Secure"/>
 </enum>
 
+<enum name="CopylessCacheHit" type="int">
+  <int value="0" label="Cache hit with entity"/>
+  <int value="1" label="Cache hit without entity"/>
+  <int value="2" label="Cache miss"/>
+</enum>
+
 <enum name="CorePageTransition" type="int">
   <summary>
     The core value of PageTransition. See ui/base/page_transition_types.h.