Oilpan: Schedule a precise GC when a page navigates

Source/platform/heap/ThreadState.h

Index: Source/platform/heap/ThreadState.h
diff --git a/Source/platform/heap/ThreadState.h b/Source/platform/heap/ThreadState.h
index 0c015aeee37db03a46d4f7c03e250cddb3e39ba8..d693c92dfdcb0b59c2e661c4a587a2b0bccac9b3 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -185,6 +185,7 @@ public:
         IdleGCScheduled,
         PreciseGCScheduled,
         FullGCScheduled,
+        PageNavigationGCScheduled,
         GCRunning,
         EagerSweepScheduled,
         LazySweepScheduled,
@@ -329,6 +330,8 @@ public:
     void scheduleIdleGC();
     void scheduleIdleLazySweep();
     void schedulePreciseGC();
+    void schedulePageNavigationGCIfNeeded(float estimatedRemovalRatio);
+    void schedulePageNavigationGC();
     void scheduleGCIfNeeded();
     void setGCState(GCState);
     GCState gcState() const;
@@ -678,6 +681,9 @@ private:
     bool shouldScheduleIdleGC();
     bool shouldSchedulePreciseGC();
     bool shouldForceConservativeGC();
+    // estimatedRemovalRatio is the estimated ratio of objects that will be no
+    // longer necessary due to the navigation.
+    bool shouldSchedulePageNavigationGC(float estimatedRemovalRatio);
 
     // Internal helper for GC policy handling code. Returns true if
     // an urgent conservative GC is now needed due to memory pressure.