Use actual incremental marking throughput in IdleNotification to estimate marking step size.

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

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_HEAP_GC_IDLE_TIME_HANDLER_H_
+#define V8_HEAP_GC_IDLE_TIME_HANDLER_H_
+
+namespace v8 {
+namespace internal {
+
+// The idle time handler makes decisions about which garbage collection
+// operations are executing during IdleNotification.
+class GCIdleTimeHandler BASE_EMBEDDED {
+ public:
+  static intptr_t EstimateMarkingStepSize(
+      int idle_time_in_ms, intptr_t marking_speed_in_bytes_per_millisecond);
+
+  // If we haven't recorded any incremental marking events yet, we carefully
+  // mark with a conservative lower bound for the marking speed.
+  static const intptr_t kInitialConservativeMarkingSpeed = 100 * KB;
+
+  // We have to make sure that we finish the IdleNotification before
+  // idle_time_in_ms. Hence, we conservatively prune our workload estimate.
+  static const double kConservativeTimeRatio;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(GCIdleTimeHandler);
+};
+}
+}  // namespace v8::internal
+
+#endif  // V8_HEAP_GC_IDLE_TIME_HANDLER_H_