Ensure nearby URL count metric is properly initialized

components/omnibox/browser/physical_web_provider.cc

 // Copyright (c) 2016 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.
 
 #include "components/omnibox/browser/physical_web_provider.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 60 matching lines @@
       client_->GetPhysicalWebDataSource();
   if (!data_source) {
     done_ = true;
     nearby_url_count_ = 0;
     return;
   }
 
   const bool input_from_focus = input.from_omnibox_focus();
   const bool empty_input_from_user = !input_from_focus && input.text().empty();
 
+  auto metadata_list = data_source->GetMetadataList();
+  nearby_url_count_ = metadata_list->size();
+
   if (input_from_focus || empty_input_from_user) {
-    ConstructZeroSuggestMatches(data_source->GetMetadataList());
+    ConstructZeroSuggestMatches(std::move(metadata_list));

[Mark P, 2017/02/11 05:17:39]

I don't understand this move operation.  Then again, I haven't thought much
about our smart pointer types in a while.  Won't this move mean you clean up the
pointer at the end of this call?  Why is that what you want?

[mattreynolds, 2017/02/13 19:00:04]

This preserves the same behavior as before. In the previous version,
GetMetadataList returns a prvalue so it didn't need std::move. Now that it has
identity, it is an xvalue and needs std::move.

Essentially, I'm choosing to be explicit that the metadata list will not be
accessed in PhysicalWebProvider::Start after we pass it to one of the
Construct.*Matches methods. As-is, the metadata list should be released when
Construct.*Matches returns. We could choose to pass a const reference instead
and then it would be cleaned up when PhysicalWebProvider::Start returns.

[Mark P, 2017/02/15 06:45:53]

Ah, okay.  Thanks for the explanation.

 
     if (!matches_.empty()) {
       had_physical_web_suggestions_ = true;
       had_physical_web_suggestions_at_focus_or_later_ = true;
     }
 
     // Don't show zero-suggest suggestions unless the PhysicalWebZeroSuggest
     // omnibox experiment parameter is enabled. If the omnibox input is empty
     // because the user cleared it, also require that PhysicalWebAfterTyping is
     // enabled.
     if (!zero_suggest_enabled_ ||
         (empty_input_from_user && !after_typing_enabled_)) {
       matches_.clear();
     }
 
     // In zero-suggest, Physical Web matches should never be default. If the
     // omnibox input is non-empty and we have at least one Physical Web match,
     // add the current URL as the default so that hitting enter after focusing
     // the omnibox causes the current page to reload. If the input field is
     // empty, no default match is required.
     if (!matches_.empty() && !input.text().empty()) {
       matches_.push_back(VerbatimMatchForURL(
           client_, input, input.current_url(), history_url_provider_, -1));
     }
   } else {
-    ConstructQuerySuggestMatches(data_source->GetMetadataList(), input);
+    ConstructQuerySuggestMatches(std::move(metadata_list), input);
 
     if (!matches_.empty()) {
       had_physical_web_suggestions_ = true;
       had_physical_web_suggestions_at_focus_or_later_ = true;
     }
 
     // Don't show Physical Web suggestions after the user starts typing unless
     // the PhysicalWebAfterTyping omnibox experiment parameter is enabled.
     if (!after_typing_enabled_) {
       matches_.clear();
@@ skipping 32 matching lines @@
   UMA_HISTOGRAM_EXACT_LINEAR("Omnibox.SuggestionUsed.NearbyURLCount",
                              nearby_url_count_, 50);
 }
 
 PhysicalWebProvider::PhysicalWebProvider(
     AutocompleteProviderClient* client,
     HistoryURLProvider* history_url_provider)
     : AutocompleteProvider(AutocompleteProvider::TYPE_PHYSICAL_WEB),
       client_(client),
       history_url_provider_(history_url_provider),
+      nearby_url_count_(0),
       zero_suggest_enabled_(
           OmniboxFieldTrial::InPhysicalWebZeroSuggestFieldTrial()),
       after_typing_enabled_(
           OmniboxFieldTrial::InPhysicalWebAfterTypingFieldTrial()),
       zero_suggest_base_relevance_(
           OmniboxFieldTrial::GetPhysicalWebZeroSuggestBaseRelevance()),
       after_typing_base_relevance_(
           OmniboxFieldTrial::GetPhysicalWebAfterTypingBaseRelevance()) {}
 
 PhysicalWebProvider::~PhysicalWebProvider() {
 }
 
 void PhysicalWebProvider::ConstructZeroSuggestMatches(
     std::unique_ptr<physical_web::MetadataList> metadata_list) {
-  nearby_url_count_ = metadata_list->size();
+  size_t nearby_url_count = metadata_list->size();
   size_t used_slots = 0;
 
-  for (size_t i = 0; i < nearby_url_count_; ++i) {
+  for (size_t i = 0; i < nearby_url_count; ++i) {
     const auto& metadata_item = (*metadata_list)[i];
     std::string url_string = metadata_item.resolved_url.spec();
     std::string title_string = metadata_item.title;
     base::string16 title =
         AutocompleteMatch::SanitizeString(base::UTF8ToUTF16(title_string));
 
     // Add match items with decreasing relevance to preserve the ordering in
     // the metadata list.
     int relevance = zero_suggest_base_relevance_ - used_slots;
 
     // Append an overflow item if creating a match for each metadata item would
     // exceed the match limit.
     const size_t remaining_slots = kPhysicalWebMaxMatches - used_slots;
-    const size_t remaining_metadata = nearby_url_count_ - i;
+    const size_t remaining_metadata = nearby_url_count - i;
     if ((remaining_slots == 1) && (remaining_metadata > remaining_slots)) {
       AppendOverflowItem(remaining_metadata, relevance, title);
       break;
     }
 
     GURL url(url_string);
 
     AutocompleteMatch match(this, relevance, false,
         AutocompleteMatchType::PHYSICAL_WEB);
     match.destination_url = url;
@@ skipping 80 matching lines @@
       AutocompleteInput::FormattedStringWithEquivalentMeaning(
           url, match.contents, client_->GetSchemeClassifier());
 
   match.description =
       l10n_util::GetStringUTF16(IDS_PHYSICAL_WEB_OVERFLOW_DESCRIPTION);
   match.description_class.push_back(
       ACMatchClassification(0, ACMatchClassification::NONE));
 
   matches_.push_back(match);
 }