Devirtualize base::BindState to save ~1% of Chrome's binary size (~1MB)

base/callback_internal.cc

Index: base/callback_internal.cc
diff --git a/base/callback_internal.cc b/base/callback_internal.cc
index f360388273dac06d9dfe4eda1a9cc737c19ee7f9..1b223172d42e4810c5fd37aae2699c9c374ec9f9 100644
--- a/base/callback_internal.cc
+++ b/base/callback_internal.cc
@@ -9,28 +9,62 @@
 namespace base {
 namespace internal {
 
-CallbackBase::CallbackBase(const CallbackBase& c) = default;
-CallbackBase& CallbackBase::operator=(const CallbackBase& c) = default;
+void BindStateBase::AddRef() {
+  AtomicRefCountInc(&ref_count_);
+}
+
+void BindStateBase::Release() {
+  if (!AtomicRefCountDec(&ref_count_))
+    destructor_(this);
+}
 
 void CallbackBase::Reset() {
-  polymorphic_invoke_ = NULL;
-  // NULL the bind_state_ last, since it may be holding the last ref to whatever
-  // object owns us, and we may be deleted after that.
-  bind_state_ = NULL;
+  polymorphic_invoke_ = nullptr;
+  // null the bind_state_ first, since it may be holding the last ref to
+  // whatever object owns us, and we may be deleted after that.
+  if (bind_state_) {
+    BindStateBase* to_release = bind_state_;
+    bind_state_ = nullptr;
+    to_release->Release();
+  }
 }
 
 bool CallbackBase::Equals(const CallbackBase& other) const {
-  return bind_state_.get() == other.bind_state_.get() &&
+  return bind_state_ == other.bind_state_ &&
          polymorphic_invoke_ == other.polymorphic_invoke_;
 }
 
+CallbackBase::CallbackBase()
+    : bind_state_(nullptr), polymorphic_invoke_(nullptr) {
+}
+
 CallbackBase::CallbackBase(BindStateBase* bind_state)
-    : bind_state_(bind_state),
-      polymorphic_invoke_(NULL) {
-  DCHECK(!bind_state_.get() || bind_state_->HasOneRef());
+    : bind_state_(bind_state) {
+  bind_state_->AddRef();
+  DCHECK_EQ(1, bind_state_->ref_count_);
+}
+
+CallbackBase::CallbackBase(const CallbackBase& c)
+    : bind_state_(c.bind_state_), polymorphic_invoke_(c.polymorphic_invoke_) {
+  if (bind_state_)
+    bind_state_->AddRef();
+}
+
+CallbackBase& CallbackBase::operator=(const CallbackBase& c) {
+  // Increment first to handle self-assignment correctly.
+  if (c.bind_state_)
+    c.bind_state_->AddRef();
+  if (bind_state_)
+    bind_state_->Release();
+
+  bind_state_ = c.bind_state_;
+  polymorphic_invoke_ = c.polymorphic_invoke_;
+  return *this;
 }
 
 CallbackBase::~CallbackBase() {
+  if (bind_state_)
+    bind_state_->Release();
 }
 
 }  // namespace internal