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

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

+// 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.
+#include <climits>
+
+#include "src/v8.h"
+
+#include "src/heap/gc-idle-time-handler.h"
+
+namespace v8 {
+namespace internal {
+
+
+const double GCIdleTimeHandler::kConservativeTimeRatio = 0.9;
+
+
+intptr_t GCIdleTimeHandler::EstimateMarkingStepSize(
+    int idle_time_in_ms, intptr_t marking_speed_in_bytes_per_ms) {
+  DCHECK(idle_time_in_ms > 0);
+
+  if (marking_speed_in_bytes_per_ms == 0) {
+    marking_speed_in_bytes_per_ms =
+        GCIdleTimeHandler::kInitialConservativeMarkingSpeed;
+  }
+
+  intptr_t marking_step_size = marking_speed_in_bytes_per_ms * idle_time_in_ms;
+  if (static_cast<intptr_t>(marking_step_size / idle_time_in_ms) !=
+      marking_speed_in_bytes_per_ms) {
+    // In the case of an overflow we return maximum marking step size.
+    return INT_MAX;
+  }
+
+  return static_cast<intptr_t>(marking_step_size *
+                               GCIdleTimeHandler::kConservativeTimeRatio);
+}
+}
+}