Make sure idle notifications perform a round of incremental GCs after context disposal.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 322a9067437217653739f95a68a8a0d3046ad3dc..e1f28bf3cf83759819600303fe0b1e59a9203945 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -4992,8 +4992,10 @@ void Heap::AdvanceIdleIncrementalMarking(intptr_t step_size) {
 
 bool Heap::IdleNotification(int hint) {
   const int kMaxHint = 1000;
-  intptr_t size_factor = Min(Max(hint, 30), kMaxHint) / 10;
-  // The size factor is in range [3..100].
+  intptr_t size_factor = Min(Max(hint, 20), kMaxHint) / 4;
+  // The size factor is in range [5..250]. The numbers here are chosen from
+  // experiments. If you changes them, make sure to test with
+  // chrome/performance_ui_tests --gtest_filter="GeneralMixMemoryTest.*
   intptr_t step_size = size_factor * IncrementalMarking::kAllocatedThreshold;
 
   if (contexts_disposed_ > 0) {
@@ -5017,11 +5019,14 @@ bool Heap::IdleNotification(int hint) {
     // Take into account that we might have decided to delay full collection
     // because incremental marking is in progress.
     ASSERT((contexts_disposed_ == 0) || !incremental_marking()->IsStopped());
+    // After context disposal there is likely a lot of garbage remaining, reset
+    // the idle notification counters in order to trigger more incremental GCs
+    // on subsequent idle notifications.
+    StartIdleRound();
     return false;
   }
 
-  if (hint >= kMaxHint || !FLAG_incremental_marking ||
-      FLAG_expose_gc || Serializer::enabled()) {
+  if (!FLAG_incremental_marking || FLAG_expose_gc || Serializer::enabled()) {
     return IdleGlobalGC();
   }
 
@@ -5060,10 +5065,6 @@ bool Heap::IdleNotification(int hint) {
   }
 
   if (incremental_marking()->IsStopped()) {
-    if (!WorthStartingGCWhenIdle()) {
-      FinishIdleRound();
-      return true;
-    }
     incremental_marking()->Start();
   }