[heap] Reland uncommit unused large object page memory.

src/base/platform/platform-macos.cc

 // Copyright 2012 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.
 
 // Platform-specific code for MacOS goes here. For the POSIX-compatible
 // parts, the implementation is in platform-posix.cc.
 
 #include <dlfcn.h>
 #include <mach/mach_init.h>
 #include <mach-o/dyld.h>
@@ skipping 221 matching lines @@
 
 bool VirtualMemory::UncommitRegion(void* address, size_t size) {
   return mmap(address,
               size,
               PROT_NONE,
               MAP_PRIVATE | MAP_ANON | MAP_NORESERVE | MAP_FIXED,
               kMmapFd,
               kMmapFdOffset) != MAP_FAILED;
 }
 
+bool VirtualMemory::ReleasePartialRegion(void* base, size_t size,
+                                         void* free_start, size_t free_size) {
+  return munmap(free_start, free_size) == 0;
+}
 
 bool VirtualMemory::ReleaseRegion(void* address, size_t size) {
   return munmap(address, size) == 0;
 }
 
 
 bool VirtualMemory::HasLazyCommits() {
   return false;
 }
 
 }  // namespace base
 }  // namespace v8