Make transition to reduce memory mode more conservative in idle time handler.

BUG=chromium:486005
LOG=NO

Review URL: https://codereview.chromium.org/1131943004

Cr-Commit-Position: refs/heads/master@{#28378}

src/heap/gc-idle-time-handler.h

@@ -158,7 +158,7 @@ class GCIdleTimeHandler {
   //    with time >= kMinLongIdleTime and without any mutator GC in between.
   static const int kMinLongIdleTime = kMaxFrameRenderingIdleTime + 1;
   static const int kLargeLongIdleTime = 900;
-  static const int kLongIdleNotificationsBeforeMutatorIsIdle = 20;
+  static const int kLongIdleNotificationsBeforeMutatorIsIdle = 600;
 
 
   class HeapState {

test/unittests/heap/gc-idle-time-handler-unittest.cc

@@ -94,7 +94,7 @@ class GCIdleTimeHandlerTest : public ::testing::Test {
   static const size_t kScavengeSpeed = 100 * KB;
   static const size_t kNewSpaceCapacity = 1 * MB;
   static const size_t kNewSpaceAllocationThroughput = 10 * KB;
-  static const int kMaxNotifications = 100;
+  static const int kMaxNotifications = 1000;
 
  private:
   GCIdleTimeHandler handler_;