Another 64->32 bit warning from the Windows compiler.

src/incremental-marking.cc

Index: src/incremental-marking.cc
===================================================================
--- src/incremental-marking.cc	(revision 9908)
+++ src/incremental-marking.cc	(working copy)
@@ -862,9 +862,9 @@
       }
     } else {
       allocation_marking_factor_ += kAllocationMarkingFactorSpeedup;
-      allocation_marking_factor_ =
+      allocation_marking_factor_ = static_cast<int>(
           Min(kMaxAllocationMarkingFactor,
-              static_cast<intptr_t>(allocation_marking_factor_ * 1.3));
+              static_cast<intptr_t>(allocation_marking_factor_ * 1.3)));
       if (FLAG_trace_gc) {
         PrintF("Marking speed increased to %d\n", allocation_marking_factor_);
       }