Oilpan: Split completeSweep() in idle tasks into chunks

Source/platform/heap/Heap.h

Index: Source/platform/heap/Heap.h
diff --git a/Source/platform/heap/Heap.h b/Source/platform/heap/Heap.h
index d9678ad0118b160615abd8f019db082ec8216d73..239d5eb7b912aeedad06e4aa8307ed0300f77aaa 100644
--- a/Source/platform/heap/Heap.h
+++ b/Source/platform/heap/Heap.h
@@ -743,6 +743,10 @@ public:
     void prepareHeapForTermination();
     void prepareForSweep();
     Address lazySweep(size_t, size_t gcInfoIndex);
+    void sweepUnsweptPage();
+    // Returns true if we have swept all pages within the deadline.
+    // Returns false otherwise.
+    bool lazySweepWithDeadline(double deadlineSeconds);
     void completeSweep();
 
     ThreadState* threadState() { return m_threadState; }