Fix Windows compile.

src/heap/gc-idle-time-handler.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/gc-idle-time-handler.h"
 #include "src/heap/gc-tracer.h"
 #include "src/utils.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 69 matching lines @@
 
   // If the limit is larger than the new space size, then scavenging used to be
   // really fast. We can take advantage of the whole new space.
   if (new_space_allocation_limit > new_space_size) {
     new_space_allocation_limit = new_space_size;
   }
 
   // We do not know the allocation throughput before the first Scavenge.
   // TODO(hpayer): Estimate allocation throughput before the first Scavenge.
   if (new_space_allocation_throughput_in_bytes_per_ms == 0) {
-    new_space_allocation_limit = new_space_size * kConservativeTimeRatio;
+    new_space_allocation_limit =
+        static_cast<size_t>(new_space_size * kConservativeTimeRatio);
   } else {
     // We have to trigger scavenge before we reach the end of new space.
     new_space_allocation_limit -=
         new_space_allocation_throughput_in_bytes_per_ms *
         kMaxFrameRenderingIdleTime;
   }
 
   if (scavenge_speed_in_bytes_per_ms == 0) {
     scavenge_speed_in_bytes_per_ms = kInitialConservativeScavengeSpeed;
   }
@@ skipping 79 matching lines @@
   if (heap_state.incremental_marking_stopped &&
       !heap_state.can_start_incremental_marking) {
     return GCIdleTimeAction::Nothing();
   }
   size_t step_size = EstimateMarkingStepSize(
       idle_time_in_ms, heap_state.incremental_marking_speed_in_bytes_per_ms);
   return GCIdleTimeAction::IncrementalMarking(step_size);
 }
 }
 }