Merge r10148 to 3.7 branch: Fix performance on the page cycler...

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index fb3ac5697939b983e958bad7495356256e556413..1b992ec44c4ac2153fc8d7083bb4544710361e84 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -3673,6 +3673,7 @@ void MarkCompactCollector::SweepSpaces() {
 #endif
   SweeperType how_to_sweep =
       FLAG_lazy_sweeping ? LAZY_CONSERVATIVE : CONSERVATIVE;
+  if (FLAG_expose_gc) how_to_sweep = CONSERVATIVE;
   if (sweep_precisely_) how_to_sweep = PRECISE;
   // Noncompacting collections simply sweep the spaces to clear the mark
   // bits and free the nonlive blocks (for old and map spaces).  We sweep