Add UMA for CopylessPaste cache

chrome/android/java/src/org/chromium/chrome/browser/AppIndexingUtil.java

Index: chrome/android/java/src/org/chromium/chrome/browser/AppIndexingUtil.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/AppIndexingUtil.java b/chrome/android/java/src/org/chromium/chrome/browser/AppIndexingUtil.java
index f0398fc37324fec487b7c25f2113939fbe54ab3f..c266d4556552d494302632938bd897033fb4664b 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/AppIndexingUtil.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/AppIndexingUtil.java
@@ -11,6 +11,7 @@ import android.webkit.URLUtil;
 import org.chromium.base.Callback;
 import org.chromium.base.SysUtils;
 import org.chromium.base.VisibleForTesting;
+import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.blink.mojom.document_metadata.CopylessPaste;
 import org.chromium.blink.mojom.document_metadata.WebPage;
 import org.chromium.chrome.browser.historyreport.AppIndexingReporter;
@@ -32,6 +33,12 @@ public class AppIndexingUtil {
 
     private static Callback<WebPage> sCallbackForTesting;
 
+    // Constants used to log UMA "enum" histograms about the cache state.

[jwd, 2017/04/19 18:49:16]

Add that the values should not be changed or reused.

+    private static final int CACHE_HIT_WITH_ENTITY = 0;
+    private static final int CACHE_HIT_WITHOUT_ENTITY = 1;
+    private static final int CACHE_MISS = 2;
+    private static final int CACHE_HISTOGRAM_BOUNDARY = 3;
+
     /**
      * Extracts entities from document metadata and reports it to on-device App Indexing.
      * This call can cache entities from recently parsed webpages, in which case, only the url and
@@ -52,11 +59,18 @@ public class AppIndexingUtil {
         if (wasPageVisitedRecently(url)) {
             if (lastPageVisitContainedEntity(url)) {
                 // Condition 1
+                RecordHistogram.recordEnumeratedHistogram(
+                        "CopylessPaste.CacheHit", CACHE_HIT_WITH_ENTITY, CACHE_HISTOGRAM_BOUNDARY);
                 getAppIndexingReporter().reportWebPageView(url, tab.getTitle());
+                return;
             }
             // Condition 2
+            RecordHistogram.recordEnumeratedHistogram(
+                    "CopylessPaste.CacheHit", CACHE_HIT_WITHOUT_ENTITY, CACHE_HISTOGRAM_BOUNDARY);
         } else {
             // Condition 3
+            RecordHistogram.recordEnumeratedHistogram(
+                    "CopylessPaste.CacheHit", CACHE_MISS, CACHE_HISTOGRAM_BOUNDARY);
             CopylessPaste copylessPaste = getCopylessPasteInterface(tab);
             if (copylessPaste == null) {
                 return;