Update from https://crrev.com/311076

base/memory/discardable_shared_memory.cc

 // Copyright 2014 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 "base/memory/discardable_shared_memory.h"
 
 #if defined(OS_POSIX)
 #include <unistd.h>
 #endif
 
@@ skipping 111 matching lines @@
   if (!checked_size.IsValid())
     return false;
 
   if (!shared_memory_.CreateAndMapAnonymous(checked_size.ValueOrDie()))
     return false;
 
   mapped_size_ =
       shared_memory_.mapped_size() - AlignToPageSize(sizeof(SharedState));
 
   locked_page_count_ = AlignToPageSize(mapped_size_) / base::GetPageSize();
-#if DCHECK_IS_ON
+#if DCHECK_IS_ON()
   for (size_t page = 0; page < locked_page_count_; ++page)
     locked_pages_.insert(page);
 #endif
 
   DCHECK(last_known_usage_.is_null());
   SharedState new_state(SharedState::LOCKED, Time());
   subtle::Release_Store(&SharedStateFromSharedMemory(shared_memory_)->value.i,
                         new_state.value.i);
   return true;
 }
 
 bool DiscardableSharedMemory::Map(size_t size) {
   if (!shared_memory_.Map(AlignToPageSize(sizeof(SharedState)) + size))
     return false;
 
   mapped_size_ =
       shared_memory_.mapped_size() - AlignToPageSize(sizeof(SharedState));
 
   locked_page_count_ = AlignToPageSize(mapped_size_) / base::GetPageSize();
-#if DCHECK_IS_ON
+#if DCHECK_IS_ON()
   for (size_t page = 0; page < locked_page_count_; ++page)
     locked_pages_.insert(page);
 #endif
 
   return true;
 }
 
 bool DiscardableSharedMemory::Lock(size_t offset, size_t length) {
   DCHECK_EQ(AlignToPageSize(offset), offset);
   DCHECK_EQ(AlignToPageSize(length), length);
@@ skipping 30 matching lines @@
     length = AlignToPageSize(mapped_size_) - offset;
 
   size_t start = offset / base::GetPageSize();
   size_t end = start + length / base::GetPageSize();
   DCHECK_LT(start, end);
   DCHECK_LE(end, AlignToPageSize(mapped_size_) / base::GetPageSize());
 
   // Add pages to |locked_page_count_|.
   // Note: Locking a page that is already locked is an error.
   locked_page_count_ += end - start;
-#if DCHECK_IS_ON
+#if DCHECK_IS_ON()
   // Detect incorrect usage by keeping track of exactly what pages are locked.
   for (auto page = start; page < end; ++page) {
     auto result = locked_pages_.insert(page);
     DCHECK(result.second);
   }
   DCHECK_EQ(locked_pages_.size(), locked_page_count_);
 #endif
 
 #if defined(OS_ANDROID)
   SharedMemoryHandle handle = shared_memory_.handle();
@@ skipping 31 matching lines @@
 
   size_t start = offset / base::GetPageSize();
   size_t end = start + length / base::GetPageSize();
   DCHECK_LT(start, end);
   DCHECK_LE(end, AlignToPageSize(mapped_size_) / base::GetPageSize());
 
   // Remove pages from |locked_page_count_|.
   // Note: Unlocking a page that is not locked is an error.
   DCHECK_GE(locked_page_count_, end - start);
   locked_page_count_ -= end - start;
-#if DCHECK_IS_ON
+#if DCHECK_IS_ON()
   // Detect incorrect usage by keeping track of exactly what pages are locked.
   for (auto page = start; page < end; ++page) {
     auto erased_count = locked_pages_.erase(page);
     DCHECK_EQ(1u, erased_count);
   }
   DCHECK_EQ(locked_pages_.size(), locked_page_count_);
 #endif
 
   // Early out and avoid releasing the platform independent lock if some pages
   // are still locked.
@@ skipping 80 matching lines @@
   SharedState result(subtle::NoBarrier_Load(
       &SharedStateFromSharedMemory(shared_memory_)->value.i));
 
   return result.GetLockState() == SharedState::LOCKED ||
          !result.GetTimestamp().is_null();
 }
 
 void DiscardableSharedMemory::Close() {
   shared_memory_.Unmap();
   shared_memory_.Close();
+  mapped_size_ = 0;
 }
 
 Time DiscardableSharedMemory::Now() const {
   return Time::Now();
 }
 
 }  // namespace base