[heap] Fix -Wsign-compare warnings

src/heap/spaces.cc

 // Copyright 2011 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/spaces.h"
 
 #include <utility>
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
@@ skipping 2834 matching lines @@
         identity(), size_in_bytes, kMaxPagesToSweep);
     RefillFreeList();
     if (max_freed >= size_in_bytes) {
       object = free_list_.Allocate(static_cast<size_t>(size_in_bytes));
       if (object != nullptr) return object;
     }
   }
 
   if (heap()->ShouldExpandOldGenerationOnAllocationFailure() && Expand()) {
     DCHECK((CountTotalPages() > 1) ||
-           (size_in_bytes <= free_list_.Available()));
+           (static_cast<size_t>(size_in_bytes) <= free_list_.Available()));
     return free_list_.Allocate(static_cast<size_t>(size_in_bytes));
   }
 
   // If sweeper threads are active, wait for them at that point and steal
   // elements form their free-lists. Allocation may still fail their which
   // would indicate that there is not enough memory for the given allocation.
   return SweepAndRetryAllocation(size_in_bytes);
 }
 
 #ifdef DEBUG
@@ skipping 366 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 }  // namespace internal
 }  // namespace v8