Add histogram to collect number of bookmarks

When profile is loaded, parse the bookmark tree to find the total count.
Adds and tests new bookmark stat, which saves to a new histogram. The
collection method is run in the profile manager class, after it has been
initialized.

Bug: 245392
Change-Id: I6a72549e2cbc197e92de4edbcf7b362212ff2c39
Reviewed-on: https://chromium-review.googlesource.com/1238901Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594540}

components/bookmarks/browser/bookmark_storage.cc

@@ -15,6 +15,7 @@
 #include "base/json/json_reader.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/numerics/safe_conversions.h"
 #include "base/sequenced_task_runner.h"
 #include "base/time/time.h"
 #include "components/bookmarks/browser/bookmark_codec.h"
@@ -115,6 +116,10 @@ void LoadBookmarks(const base::FilePath& path, BookmarkLoadDetails* details) {
   }
 
   details->CreateUrlIndex();
+
+  UMA_HISTOGRAM_COUNTS_100000(
+      "Bookmarks.Count.OnProfileLoad",
+      base::saturated_cast<int>(details->url_index()->UrlCount()));
 }
 
 // BookmarkLoadDetails ---------------------------------------------------------

components/bookmarks/browser/url_index.cc

@@ -71,11 +71,16 @@ void UrlIndex::GetNodesByUrl(const GURL& url,
   }
 }
 
-bool UrlIndex::HasBookmarks() {
+bool UrlIndex::HasBookmarks() const {
   base::AutoLock url_lock(url_lock_);
   return !nodes_ordered_by_url_set_.empty();
 }
 
+size_t UrlIndex::UrlCount() const {
+  base::AutoLock url_lock(url_lock_);
+  return nodes_ordered_by_url_set_.size();
+}
+
 bool UrlIndex::IsBookmarked(const GURL& url) {
   base::AutoLock url_lock(url_lock_);
   return IsBookmarkedNoLock(url);

components/bookmarks/browser/url_index.h

@@ -56,7 +56,10 @@ class UrlIndex : public HistoryBookmarkModel {
   void GetNodesByUrl(const GURL& url, std::vector<const BookmarkNode*>* nodes);
 
   // Returns true if there is at least one bookmark.
-  bool HasBookmarks();
+  bool HasBookmarks() const;
+
+  // Returns the number of URL bookmarks stored.
+  size_t UrlCount() const;
 
   // HistoryBookmarkModel:
   bool IsBookmarked(const GURL& url) override;
@@ -88,7 +91,7 @@ class UrlIndex : public HistoryBookmarkModel {
   // such, be sure and wrap all usage of it around |url_lock_|.
   using NodesOrderedByUrlSet = std::multiset<BookmarkNode*, NodeUrlComparator>;
   NodesOrderedByUrlSet nodes_ordered_by_url_set_;
-  base::Lock url_lock_;
+  mutable base::Lock url_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(UrlIndex);
 };

tools/metrics/histograms/histograms.xml

@@ -10797,6 +10797,19 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="Bookmarks.Count.OnProfileLoad" units="bookmarks"
+    expires_after="2019-03-24">
+  <owner>supertri@chromium.org</owner>
+  <owner>isherman@chromium.org</owner>
+  <owner>aidanday@google.com</owner>
+  <summary>
+    The total number of bookmarks a user has saved. Recorded when a profile is
+    opened - precisely, when bookmarks are loaded into storage from disk. The
+    count includes all bookmarks both in the &quot;Bookmarks Bar&quot; and also
+    under &quot;Other Bookmarks&quot;.
+  </summary>
+</histogram>
+
 <histogram name="Bookmarks.EntryPoint" enum="BookmarksEntryPoint">
   <owner>ianwen@chromium.org</owner>
   <summary>How users add a new bookmark.</summary>