[omnibox] [max-suggest] Add dynamic suggestions limit per # of URLs.

Follow up to crrev.com/c/2274466 . The previous CL updated the
autocomplete results to conditionally boost the max suggestions.
However, the search provider limits the # of suggestions it provides to
the unboosted limit, rendering the boost ineffective.

This CL updates the search provider to send the max of GetMaxMatches
(e.g. 8) and kDynamicMaxAutocompleteIncreasedLimitParam (e.g. 10).

Change-Id: Iaa9933b4445874488d42d831d76ef30a2d9e3e8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2293458Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: manuk hovanesian <manukh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#787856}

components/omnibox/browser/autocomplete_result.cc

@@ -112,6 +112,14 @@ size_t AutocompleteResult::GetMaxMatches(bool input_from_omnibox_focus) {
   return field_trial_value;
 }
 
+// static
+size_t AutocompleteResult::GetDynamicMaxMatches() {
+  return base::GetFieldTrialParamByFeatureAsInt(
+      omnibox::kDynamicMaxAutocomplete,
+      OmniboxFieldTrial::kDynamicMaxAutocompleteIncreasedLimitParam,
+      AutocompleteResult::GetMaxMatches());
+}
+
 AutocompleteResult::AutocompleteResult() {
   // Reserve enough space for the maximum number of matches we'll show in either
   // on-focus or prefix-suggest mode.
@@ -639,13 +647,11 @@ size_t AutocompleteResult::CalculateNumMatchesPerUrlCount(
     const ACMatches& matches,
     const CompareWithDemoteByType<AutocompleteMatch>& comparing_object) {
   size_t base_limit = GetMaxMatches();
+  size_t increased_limit = GetDynamicMaxMatches();
   size_t url_cutoff = base::GetFieldTrialParamByFeatureAsInt(
       omnibox::kDynamicMaxAutocomplete,
       OmniboxFieldTrial::kDynamicMaxAutocompleteUrlCutoffParam, 0);
-  size_t increased_limit = base::GetFieldTrialParamByFeatureAsInt(
-      omnibox::kDynamicMaxAutocomplete,
-      OmniboxFieldTrial::kDynamicMaxAutocompleteIncreasedLimitParam,
-      base_limit);
+  DCHECK(increased_limit > base_limit);
 
   size_t num_matches = 0;
   size_t num_url_matches = 0;

components/omnibox/browser/autocomplete_result.h

@@ -33,8 +33,12 @@ class AutocompleteResult {
 
   // Max number of matches we'll show from the various providers. This limit may
   // be different for zero suggest (i.e. when |input_from_omnibox_focus| is
-  // true) and non zero suggest.
+  // true) and non zero suggest. Does not take into account the boost
+  // conditionally provided by the omnibox::kDynamicMaxAutocomplete feature.
   static size_t GetMaxMatches(bool input_from_omnibox_focus = false);
+  // Defaults to GetMaxMatches if omnibox::kDynamicMaxAutocomplete is disabled;
+  // otherwise returns the boosted dynamic limit.
+  static size_t GetDynamicMaxMatches();
 
   AutocompleteResult();
   ~AutocompleteResult();

components/omnibox/browser/search_provider.cc

@@ -1090,12 +1090,13 @@ void SearchProvider::ConvertResultsToAutocompleteMatches() {
   // always include in that set a legal default match if possible.  If Instant
   // Extended is enabled and we have server-provided (and thus hopefully more
   // accurate) scores for some suggestions, we allow more of those, until we
-  // reach AutocompleteResult::GetMaxMatches() total matches (that is, enough to
-  // fill the whole popup).
+  // reach AutocompleteResult::GetDynamicMaxMatches() total matches (that is,
+  // enough to fill the whole popup).
   //
   // We will always return any verbatim matches, no matter how we obtained their
-  // scores, unless we have already accepted AutocompleteResult::GetMaxMatches()
-  // higher-scoring matches under the conditions above.
+  // scores, unless we have already accepted
+  // AutocompleteResult::GetDynamicMaxMatches() higher-scoring matches under
+  // the conditions above.
   std::sort(matches.begin(), matches.end(), &AutocompleteMatch::MoreRelevant);
 
   // Guarantee that if there's a legal default match anywhere in the result
@@ -1117,7 +1118,7 @@ void SearchProvider::ConvertResultsToAutocompleteMatches() {
   size_t num_suggestions = 0;
   for (ACMatches::const_iterator i(matches.begin());
        (i != matches.end()) &&
-       (matches_.size() < AutocompleteResult::GetMaxMatches());
+       (matches_.size() < AutocompleteResult::GetDynamicMaxMatches());
        ++i) {
     // SEARCH_OTHER_ENGINE is only used in the SearchProvider for the keyword
     // verbatim result, so this condition basically means "if this match is a
@@ -1612,7 +1613,7 @@ void SearchProvider::PrefetchImages(SearchSuggestionParser::Results* results) {
   // are processed in descending order of relevance so the first suggestions are
   // the ones to be shown; prefetching images for the rest would be wasteful.
   std::vector<GURL> prefetch_image_urls;
-  int prefetch_limit = AutocompleteResult::GetMaxMatches();
+  int prefetch_limit = AutocompleteResult::GetDynamicMaxMatches();
   for (const auto& suggestion : results->suggest_results) {
     if (prefetch_limit <= 0)
       break;