Add some support for promptly purging pages.

third_party/WebKit/Source/platform/heap/PageMemory.cpp

 // Copyright 2016 The Chromium 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 "platform/heap/PageMemory.h"
 
 #include "platform/heap/Heap.h"
 #include "platform/wtf/AddressSanitizer.h"
 #include "platform/wtf/Assertions.h"
 #include "platform/wtf/Atomics.h"
 
 namespace blink {
 
 void MemoryRegion::Release() {
   WTF::FreePages(base_, size_);
 }
 
 bool MemoryRegion::Commit() {
   WTF::RecommitSystemPages(base_, size_);
   return WTF::SetSystemPagesAccessible(base_, size_);
 }
 
-void MemoryRegion::Decommit() {
+void MemoryRegion::Decommit(DecommitMemoryTiming decommit_hint) {
   ASAN_UNPOISON_MEMORY_REGION(base_, size_);
-  WTF::DecommitSystemPages(base_, size_);
+  WTF::DecommitSystemPages(
+      base_, size_, decommit_hint == DecommitMemoryTiming::DecommitPromptly);
   WTF::SetSystemPagesInaccessible(base_, size_);
 }
 
 PageMemoryRegion::PageMemoryRegion(Address base,
                                    size_t size,
                                    unsigned num_pages,
                                    RegionTree* region_tree)
     : MemoryRegion(base, size),
       is_large_page_(num_pages == 1),
       num_pages_(num_pages),
@@ skipping 133 matching lines @@
   size_t allocation_size = payload_size + 2 * kBlinkGuardPageSize;
   PageMemoryRegion* page_memory_region =
       PageMemoryRegion::AllocateLargePage(allocation_size, region_tree);
   PageMemory* storage =
       SetupPageMemoryInRegion(page_memory_region, 0, payload_size);
   CHECK(storage->Commit());
   return storage;
 }
 
 }  // namespace blink