Adjust small heap threshold for idle time handler.

Follow-up for r23871.

BUG=chromium:407593
LOG=N
TBR=hpayer@chromium.org

Review URL: https://codereview.chromium.org/592053002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24116 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

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

@@ -108,7 +108,7 @@ class GCIdleTimeHandler {
 
   // Heap size threshold below which we prefer mark-compact over incremental
   // step.
-  static const size_t kSmallHeapSize = 2 * kPointerSize * MB;
+  static const size_t kSmallHeapSize = 4 * kPointerSize * MB;
 
   // That is the maximum idle time we will have during frame rendering.
   static const size_t kMaxFrameRenderingIdleTime = 16;