Fix a compiler error on Windows introduced by r10093

BUG=
TEST=

Review URL: http://codereview.chromium.org/8749008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10100 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/incremental-marking.cc

@@ -773,7 +773,7 @@ void IncrementalMarking::Step(intptr_t allocated_bytes) {
   }
 
   if (state_ == SWEEPING) {
-    if (heap_->AdvanceSweepers(bytes_to_process)) {
+    if (heap_->AdvanceSweepers(static_cast<int>(bytes_to_process))) {
       bytes_scanned_ = 0;
       StartMarking(PREVENT_COMPACTION);
     }