Revert of Make base::WeakPtr::Get() fast

base/memory/weak_ptr.cc

 // Copyright (c) 2011 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/weak_ptr.h"
 
-#include "base/debug/leak_annotations.h"
-
 namespace base {
 namespace internal {
 
-static constexpr uintptr_t kTrueMask = ~static_cast<uintptr_t>(0);
-
-WeakReference::Flag::Flag() : is_valid_(kTrueMask) {
-#if DCHECK_IS_ON()
+WeakReference::Flag::Flag() : is_valid_(true) {
   // Flags only become bound when checked for validity, or invalidated,
   // so that we can check that later validity/invalidation operations on
   // the same Flag take place on the same sequenced thread.
   sequence_checker_.DetachFromSequence();
-#endif
 }
 
-WeakReference::Flag::Flag(WeakReference::Flag::NullFlagTag) : is_valid_(false) {
-  // There is no need for sequence_checker_.DetachFromSequence() because the
-  // null flag doesn't participate in the sequence checks. See DCHECK in
-  // Invalidate() and IsValid().
-
-  // Keep the object alive perpetually, even when there are no references to it.
-  AddRef();
+void WeakReference::Flag::Invalidate() {
+  // The flag being invalidated with a single ref implies that there are no
+  // weak pointers in existence. Allow deletion on other thread in this case.
+  DCHECK(sequence_checker_.CalledOnValidSequence() || HasOneRef())
+      << "WeakPtrs must be invalidated on the same sequenced thread.";
+  is_valid_ = false;
 }
 
-WeakReference::Flag* WeakReference::Flag::NullFlag() {
-  ANNOTATE_SCOPED_MEMORY_LEAK;
-  static Flag* g_null_flag = new Flag(kNullFlagTag);
-  return g_null_flag;
+bool WeakReference::Flag::IsValid() const {
+  DCHECK(sequence_checker_.CalledOnValidSequence())
+      << "WeakPtrs must be checked on the same sequenced thread.";
+  return is_valid_;
 }
 
-WeakReference::Flag::~Flag() {}
+WeakReference::Flag::~Flag() {
+}
 
-WeakReference::WeakReference() : flag_(Flag::NullFlag()) {}
+WeakReference::WeakReference() {
+}
+
+WeakReference::WeakReference(const Flag* flag) : flag_(flag) {
+}
 
 WeakReference::~WeakReference() {
 }
 
-WeakReference::WeakReference(const Flag* flag) : flag_(flag) {}
-
-WeakReference::WeakReference(WeakReference&& other)
-    : flag_(std::move(other.flag_)) {
-  other.flag_ = Flag::NullFlag();
-}
+WeakReference::WeakReference(WeakReference&& other) = default;
 
 WeakReference::WeakReference(const WeakReference& other) = default;
 
-WeakReferenceOwner::WeakReferenceOwner()
-    : flag_(WeakReference::Flag::NullFlag()) {}
+bool WeakReference::is_valid() const { return flag_.get() && flag_->IsValid(); }
+
+WeakReferenceOwner::WeakReferenceOwner() {
+}
 
 WeakReferenceOwner::~WeakReferenceOwner() {
   Invalidate();
 }
 
 WeakReference WeakReferenceOwner::GetRef() const {
   // If we hold the last reference to the Flag then create a new one.
   if (!HasRefs())
     flag_ = new WeakReference::Flag();
 
   return WeakReference(flag_.get());
 }
 
 void WeakReferenceOwner::Invalidate() {
-  flag_->Invalidate();
-  flag_ = WeakReference::Flag::NullFlag();
+  if (flag_.get()) {
+    flag_->Invalidate();
+    flag_ = NULL;
+  }
 }
 
 WeakPtrBase::WeakPtrBase() : ptr_(0) {}
 
 WeakPtrBase::~WeakPtrBase() {}
 
 WeakPtrBase::WeakPtrBase(const WeakReference& ref, uintptr_t ptr)
     : ref_(ref), ptr_(ptr) {}
 
 WeakPtrFactoryBase::WeakPtrFactoryBase(uintptr_t ptr) : ptr_(ptr) {}
 
 WeakPtrFactoryBase::~WeakPtrFactoryBase() {
   ptr_ = 0;
 }
 
 }  // namespace internal
 }  // namespace base