Oilpan: Reenable a threshold for page navigation GCs

https://codereview.chromium.org/1287283002/ unintentionally removed code
to consider estimatedRemovalRate when judging a threshold for page navigation GCs.
This CL recovers the code.

BUG=474470

Review URL: https://codereview.chromium.org/1301893003

git-svn-id: svn://svn.chromium.org/blink/trunk@200876 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/platform/heap/ThreadState.cpp

@@ -659,7 +659,7 @@ bool ThreadState::shouldSchedulePreciseGC()
 
 bool ThreadState::shouldSchedulePageNavigationGC(float estimatedRemovalRatio)
 {
-    return judgeGCThreshold(1024 * 1024, 1.5);
+    return judgeGCThreshold(1024 * 1024, 1.5 * (1 - estimatedRemovalRatio));
 }
 
 bool ThreadState::shouldForceConservativeGC()