Do not pause/resume background tab opening based on memory pressure signal

Memory signal is currently unreliable. We should not pause or resume
background tab opening based on the memory pressure signal.

Bug: 762775,730098
Change-Id: Ic976493bb7af94c451d54e8c8f655dbdd6b2421e
Reviewed-on: https://chromium-review.googlesource.com/736869Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Commit-Queue: Zhen Wang <zhenw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512863}

chrome/browser/resource_coordinator/tab_manager.cc

@@ -962,15 +962,14 @@ void TabManager::OnMemoryPressure(
   if (g_browser_process->IsShuttingDown())
     return;
 
+  // TODO(crbug.com/762775): Pause or resume background tab opening based on
+  // memory pressure signal after it becomes more reliable.
   switch (memory_pressure_level) {
     case base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE:
-      ResumeBackgroundTabOpeningIfNeeded();
       break;
     case base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE:
-      PauseBackgroundTabOpeningIfNeeded();
       break;
     case base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL:
-      PauseBackgroundTabOpeningIfNeeded();
       LogMemoryAndDiscardTab(kUrgentShutdown);
       break;
     default:

chrome/browser/resource_coordinator/tab_manager_unittest.cc

@@ -942,10 +942,8 @@ TEST_F(TabManagerTest, BackgroundTabLoadingMode) {
   EXPECT_TRUE(tab_manager->IsNavigationDelayedForTest(nav_handle2_.get()));
   EXPECT_TRUE(tab_manager->IsNavigationDelayedForTest(nav_handle3_.get()));
 
-  // Simulate memory pressure getting high. TabManager pause loading pending
-  // background tabs.
-  tab_manager->OnMemoryPressure(
-      base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE);
+  // TabManager pauses loading pending background tabs.
+  tab_manager->PauseBackgroundTabOpeningIfNeeded();
   EXPECT_EQ(TabManager::BackgroundTabLoadingMode::kPaused,
             tab_manager->background_tab_loading_mode_);
 
@@ -968,10 +966,8 @@ TEST_F(TabManagerTest, BackgroundTabLoadingMode) {
   EXPECT_TRUE(tab_manager->IsNavigationDelayedForTest(nav_handle2_.get()));
   EXPECT_TRUE(tab_manager->IsNavigationDelayedForTest(nav_handle3_.get()));
 
-  // Simulate memory pressure is relieved. TabManager will reset the loading
-  // mode and try to load the next tab.
-  tab_manager->OnMemoryPressure(
-      base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE);
+  // TabManager resumes loading pending background tabs.
+  tab_manager->ResumeBackgroundTabOpeningIfNeeded();
   EXPECT_EQ(TabManager::BackgroundTabLoadingMode::kStaggered,
             tab_manager->background_tab_loading_mode_);
 
@@ -1059,10 +1055,8 @@ TEST_F(TabManagerTest, PauseAndResumeBackgroundTabOpening) {
   EXPECT_TRUE(
       tab_manager->stats_collector()->is_in_background_tab_opening_session());
 
-  // Simulate memory pressure getting high. TabManager pause loading pending
-  // background tabs, and ends the background tab opening session.
-  tab_manager->OnMemoryPressure(
-      base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE);
+  // TabManager pauses loading pending background tabs.
+  tab_manager->PauseBackgroundTabOpeningIfNeeded();
   EXPECT_EQ(TabManager::BackgroundTabLoadingMode::kPaused,
             tab_manager->background_tab_loading_mode_);
   EXPECT_FALSE(tab_manager->IsInBackgroundTabOpeningSession());
@@ -1082,11 +1076,8 @@ TEST_F(TabManagerTest, PauseAndResumeBackgroundTabOpening) {
   EXPECT_FALSE(
       tab_manager->stats_collector()->is_in_background_tab_opening_session());
 
-  // Simulate memory pressure is relieved. TabManager will reset the loading
-  // mode and try to load the next tab. If there is pending tab, TabManager
-  // starts a new BackgroundTabOpening session.
-  tab_manager->OnMemoryPressure(
-      base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE);
+  // TabManager resumes loading pending background tabs.
+  tab_manager->ResumeBackgroundTabOpeningIfNeeded();
   EXPECT_EQ(TabManager::BackgroundTabLoadingMode::kStaggered,
             tab_manager->background_tab_loading_mode_);
   EXPECT_TRUE(tab_manager->IsInBackgroundTabOpeningSession());