Shrinking of PagedSpace is done only by sweeper.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index b6ef3f58dcadb70b735ac2914cd54464c77820ab..49c1692e63c8dfcecfce932bb13a6e0c02cbf6c7 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -591,7 +591,6 @@ void Heap::CollectAllAvailableGarbage(const char* gc_reason) {
   mark_compact_collector()->SetFlags(kNoGCFlags);
   new_space_.Shrink();
   UncommitFromSpace();
-  Shrink();
   incremental_marking()->UncommitMarkingDeque();
 }
 
@@ -789,11 +788,6 @@ void Heap::EnsureFromSpaceIsCommitted() {
   if (new_space_.CommitFromSpaceIfNeeded()) return;
 
   // Committing memory to from space failed.
-  // Try shrinking and try again.
-  Shrink();
-  if (new_space_.CommitFromSpaceIfNeeded()) return;
-
-  // Committing memory to from space failed again.
   // Memory is exhausted and we will die.
   V8::FatalProcessOutOfMemory("Committing semi space failed.");
 }
@@ -822,7 +816,6 @@ void Heap::ClearJSFunctionResultCaches() {
 }
 
 
-
 void Heap::ClearNormalizedMapCaches() {
   if (isolate_->bootstrapper()->IsActive() &&
       !incremental_marking()->IsMarking()) {
@@ -6414,17 +6407,6 @@ void Heap::TearDown() {
 }
 
 
-void Heap::Shrink() {
-  // Try to shrink all paged spaces.
-  PagedSpaces spaces(this);
-  for (PagedSpace* space = spaces.next();
-       space != NULL;
-       space = spaces.next()) {
-    space->ReleaseAllUnusedPages();
-  }
-}
-
-
 void Heap::AddGCPrologueCallback(GCPrologueCallback callback, GCType gc_type) {
   ASSERT(callback != NULL);
   GCPrologueCallbackPair pair(callback, gc_type);