[heap] Reland uncommit unused large object page memory.

src/base/platform/platform-linux.cc

Index: src/base/platform/platform-linux.cc
diff --git a/src/base/platform/platform-linux.cc b/src/base/platform/platform-linux.cc
index 1323a0dd91efc1751ea17b163f0ff0ae4c3095c6..f00acf1892c50029b28a6e20a33a80e3f8e2e090 100644
--- a/src/base/platform/platform-linux.cc
+++ b/src/base/platform/platform-linux.cc
@@ -375,6 +375,14 @@ bool VirtualMemory::UncommitRegion(void* base, size_t size) {
               kMmapFdOffset) != MAP_FAILED;
 }
 
+bool VirtualMemory::ReleasePartialRegion(void* base, size_t size,
+                                         void* free_start, size_t free_size) {
+#if defined(LEAK_SANITIZER)
+  __lsan_unregister_root_region(base, size);
+  __lsan_register_root_region(base, size - free_size);
+#endif
+  return munmap(free_start, free_size) == 0;
+}
 
 bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
 #if defined(LEAK_SANITIZER)