make gc branch compile on Win32.

src/incremental-marking.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 549 matching lines @@
     if (marking_deque_.IsEmpty()) MarkingComplete();
   }
 
   allocated_ = 0;
 
   steps_count_++;
   steps_count_since_last_gc_++;
 
   if ((steps_count_ % kAllocationMarkingFactorSpeedupInterval) == 0) {
     allocation_marking_factor_ += kAllocationMarkingFactorSpeedup;
-    allocation_marking_factor_ *= 1.3;
+    allocation_marking_factor_ =
+        static_cast<int>(allocation_marking_factor_ * 1.3);
     if (FLAG_trace_gc) {
       PrintF("Marking speed increased to %d\n", allocation_marking_factor_);
     }
   }
 
   if (FLAG_trace_incremental_marking || FLAG_trace_gc) {
     double end = OS::TimeCurrentMillis();
     double delta = (end - start);
     steps_took_ += delta;
     steps_took_since_last_gc_ += delta;
   }
 }
 
 
 } }  // namespace v8::internal