Tabdiscarder: explore process_types to be scored by tabranker.

This change gives us the ability to explore different process_types to
be scored by TabRanker. We can try
(1) to only discard BACKGROUND tabs. or
(2) to discard BACKGROUND and PROTECTED_BACKGROUND tabs.

Bug: 968391
Change-Id: Idb65c1609ce81aa5c8c3a0b07c8cab1a016384d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1633872Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Charles . <charleszhao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665004}

chrome/browser/resource_coordinator/tab_manager_delegate_chromeos.cc

@@ -553,12 +553,16 @@ void TabManagerDelegate::SortLifecycleUnitWithTabRanker(
   const uint32_t num_of_tab_to_score = GetNumOldestTabsToScoreWithTabRanker();
   if (num_of_tab_to_score <= 1)
     return;
+
+  const ProcessType process_type =
+      static_cast<ProcessType>(GetProcessTypeToScoreWithTabRanker());
+
   // Put the oldest num_of_tab_to_score lifecycle units into a vector.
   LifecycleUnitVector oldest_lifecycle_units;
   for (auto it = candidates->rbegin(); it != candidates->rend(); ++it) {
     auto& candidate = *it;
     if (oldest_lifecycle_units.size() == num_of_tab_to_score ||
-        candidate.process_type() < ProcessType::BACKGROUND)
+        candidate.process_type() < process_type)
       break;
     if (candidate.lifecycle_unit()) {
       oldest_lifecycle_units.push_back(candidate.lifecycle_unit());
@@ -572,7 +576,7 @@ void TabManagerDelegate::SortLifecycleUnitWithTabRanker(
   for (auto it = candidates->rbegin(); it != candidates->rend(); ++it) {
     const auto& candidate = *it;
     if (oldest_lifecycle_units.empty() ||
-        candidate.process_type() < ProcessType::BACKGROUND)
+        candidate.process_type() < process_type)
       break;
     if (candidate.lifecycle_unit()) {
       *it = Candidate(oldest_lifecycle_units.back());

chrome/browser/resource_coordinator/tab_manager_features.cc

@@ -262,6 +262,11 @@ int GetNumOldestTabsToScoreWithTabRanker() {
       std::numeric_limits<int>::max());
 }
 
+int GetProcessTypeToScoreWithTabRanker() {
+  return base::GetFieldTrialParamByFeatureAsInt(
+      features::kTabRanker, "process_type_of_tabs_to_score_with_TabRanker", 4);
+}
+
 int GetNumOldestTabsToLogWithTabRanker() {
   return base::GetFieldTrialParamByFeatureAsInt(
       features::kTabRanker, "number_of_oldest_tabs_to_log_with_TabRanker", 0);

chrome/browser/resource_coordinator/tab_manager_features.h

@@ -267,6 +267,9 @@ GetStaticSiteCharacteristicsDatabaseParams();
 // Gets number of oldest tab that should be scored by TabRanker.
 int GetNumOldestTabsToScoreWithTabRanker();
 
+// Gets ProcessType of tabs that should be scored by TabRanker.
+int GetProcessTypeToScoreWithTabRanker();
+
 // Gets number of oldest tabs that should be logged by TabRanker.
 int GetNumOldestTabsToLogWithTabRanker();