Add UMA for CopylessPaste cache

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

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser;
 
 import android.os.SystemClock;
 import android.util.LruCache;
 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;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.content_public.browser.RenderFrameHost;
 import org.chromium.content_public.browser.WebContents;
 import org.chromium.services.service_manager.InterfaceProvider;
 
 /**
  * This is the top-level CopylessPaste metadata extraction for AppIndexing.
  */
 public class AppIndexingUtil {
     private static final int CACHE_SIZE = 100;
     private static final int CACHE_VISIT_CUTOFF_MS = 60 * 60 * 1000; // 1 hour
     // Cache of recently seen urls. If a url is among the CACHE_SIZE most recent pages visited, and
     // the parse was in the last CACHE_VISIT_CUTOFF_MS milliseconds, then we don't parse the page,
     // and instead just report the view (not the content) to App Indexing.
     private LruCache<String, CacheEntry> mPageCache;
 
     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
      * title of the page is reported to App Indexing.
      */
     public void extractCopylessPasteMetadata(final Tab tab) {
         final String url = tab.getUrl();
         boolean isHttpOrHttps = URLUtil.isHttpsUrl(url) || URLUtil.isHttpUrl(url);
         if (!isEnabledForDevice() || tab.isIncognito() || !isHttpOrHttps) {
             return;
         }
 
         // There are three conditions that can occur with respect to the cache.
         // 1. Cache hit, and an entity was found previously. Report only the page view to App
         //    Indexing.
         // 2. Cache hit, but no entity was found. Ignore.
         // 3. Cache miss, we need to parse the page.
         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;
             }
             copylessPaste.getEntities(new CopylessPaste.GetEntitiesResponse() {
                 @Override
                 public void call(WebPage webpage) {
                     putCacheEntry(url, webpage != null);
                     if (sCallbackForTesting != null) {
                         sCallbackForTesting.onResult(webpage);
@@ skipping 77 matching lines @@
             mPageCache = new LruCache<String, CacheEntry>(CACHE_SIZE);
         }
         return mPageCache;
     }
 
     private static class CacheEntry {
         public long lastSeenTimeMs;
         public boolean containedEntity;
     }
 }