[RC] Allow repeated discards.

Allow tabs to be discarded more than once. The heuristics have changed
so much in in the last 6 months that this additional protection isn't
needed.

BUG=794622

Change-Id: I094af452b5a7190f229fefbc77f4571ac0601a17
Reviewed-on: https://chromium-review.googlesource.com/1142479
Commit-Queue: Chris Hamilton <chrisha@chromium.org>
Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576485}

chrome/browser/resource_coordinator/tab_lifecycle_unit.cc

@@ -532,23 +532,6 @@ bool TabLifecycleUnitSource::TabLifecycleUnit::CanDiscard(
     return false;
   }
 
-  // Do not discard a tab that has already been discarded. Since this is being
-  // removed there is no way to communicate that to the heuristic. Treat this
-  // as a "trivial" rejection reason for now and return with an empty decision
-  // details.
-  // TODO(fdoray): Allow tabs to be discarded more than once.
-  // https://crbug.com/794622
-  if (discard_count_ > 0) {
-#if defined(OS_CHROMEOS)
-    // On ChromeOS this can be ignored for urgent discards, where running out of
-    // memory leads to a kernel panic.
-    if (reason != DiscardReason::kUrgent)
-      return false;
-#else
-    return false;
-#endif  // defined(OS_CHROMEOS)
-  }
-
   // We deliberately run through all of the logic without early termination.
   // This ensures that the decision details lists all possible reasons that the
   // transition can be denied.

chrome/browser/resource_coordinator/tab_lifecycle_unit_source_unittest.cc

@@ -413,58 +413,6 @@ class TabLifecycleUnitSourceTest
                     .GetPendingEntry());
   }
 
-  void CanOnlyDiscardOnceTest(DiscardReason reason) {
-    LifecycleUnit* background_lifecycle_unit = nullptr;
-    LifecycleUnit* foreground_lifecycle_unit = nullptr;
-    CreateTwoTabs(true /* focus_tab_strip */, &background_lifecycle_unit,
-                  &foreground_lifecycle_unit);
-    content::WebContents* initial_web_contents =
-        tab_strip_model_->GetWebContentsAt(0);
-
-    // It should be possible to discard the background tab.
-    ExpectCanDiscardTrueAllReasons(background_lifecycle_unit);
-
-    // Discard the tab.
-    EXPECT_EQ(LifecycleUnitState::ACTIVE,
-              background_lifecycle_unit->GetState());
-    EXPECT_CALL(tab_observer_, OnDiscardedStateChange(::testing::_, true));
-    background_lifecycle_unit->Discard(reason);
-
-    ::testing::Mock::VerifyAndClear(&tab_observer_);
-
-    TransitionFromPendingDiscardToDiscardedIfNeeded(reason,
-                                                    background_lifecycle_unit);
-
-    EXPECT_NE(initial_web_contents, tab_strip_model_->GetWebContentsAt(0));
-    EXPECT_FALSE(tab_strip_model_->GetWebContentsAt(0)
-                     ->GetController()
-                     .GetPendingEntry());
-
-    // Explicitly reload the tab. Expect the state to be LOADED.
-    EXPECT_CALL(tab_observer_, OnDiscardedStateChange(::testing::_, false));
-    tab_strip_model_->GetWebContentsAt(0)->GetController().Reload(
-        content::ReloadType::NORMAL, false);
-    ::testing::Mock::VerifyAndClear(&tab_observer_);
-    EXPECT_EQ(LifecycleUnitState::ACTIVE,
-              background_lifecycle_unit->GetState());
-    EXPECT_TRUE(tab_strip_model_->GetWebContentsAt(0)
-                    ->GetController()
-                    .GetPendingEntry());
-
-    // It shouldn't be possible to discard the background tab again, except for
-    // an urgent discard on ChromeOS.
-    ExpectCanDiscardFalseTrivial(background_lifecycle_unit,
-                                 DiscardReason::kExternal);
-    ExpectCanDiscardFalseTrivial(background_lifecycle_unit,
-                                 DiscardReason::kProactive);
-#if defined(OS_CHROMEOS)
-    ExpectCanDiscardTrue(background_lifecycle_unit, DiscardReason::kUrgent);
-#else
-    ExpectCanDiscardFalseTrivial(background_lifecycle_unit,
-                                 DiscardReason::kUrgent);
-#endif
-  }
-
   TabLifecycleUnitSource* source_ = nullptr;
   ::testing::StrictMock<MockLifecycleUnitSourceObserver> source_observer_;
   ::testing::StrictMock<MockTabLifecycleObserver> tab_observer_;
@@ -645,18 +593,6 @@ TEST_F(TabLifecycleUnitSourceTest, DiscardAndExplicitlyReload_External) {
   DiscardAndExplicitlyReloadTest(DiscardReason::kExternal);
 }
 
-TEST_F(TabLifecycleUnitSourceTest, CanOnlyDiscardOnce_Urgent) {
-  CanOnlyDiscardOnceTest(DiscardReason::kUrgent);
-}
-
-TEST_F(TabLifecycleUnitSourceTest, CanOnlyDiscardOnce_Proactive) {
-  CanOnlyDiscardOnceTest(DiscardReason::kProactive);
-}
-
-TEST_F(TabLifecycleUnitSourceTest, CanOnlyDiscardOnce_External) {
-  CanOnlyDiscardOnceTest(DiscardReason::kExternal);
-}
-
 TEST_F(TabLifecycleUnitSourceTest, CannotFreezeADiscardedTab) {
   LifecycleUnit* background_lifecycle_unit = nullptr;
   LifecycleUnit* foreground_lifecycle_unit = nullptr;