Base: Bind SupportsWeakPtr's references to the constructor's thread.

base/memory/weak_ptr.cc

Index: base/memory/weak_ptr.cc
diff --git a/base/memory/weak_ptr.cc b/base/memory/weak_ptr.cc
index d9ce86ad18901a0719255c031fae1a1357ad1f2f..2eaa6ea4cfc6f7ee97eb426a9ee0650a5ccfbdc3 100644
--- a/base/memory/weak_ptr.cc
+++ b/base/memory/weak_ptr.cc
@@ -7,11 +7,13 @@
 namespace base {
 namespace internal {
 
-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();
+WeakReference::Flag::Flag(bool bound_to_current_sequence) : is_valid_(true) {
+  if (!bound_to_current_sequence) {
+    // 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();
+  }
 }
 
 void WeakReference::Flag::Invalidate() {
@@ -42,7 +44,10 @@ WeakReference::~WeakReference() {
 
 bool WeakReference::is_valid() const { return flag_.get() && flag_->IsValid(); }
 
-WeakReferenceOwner::WeakReferenceOwner() {
+WeakReferenceOwner::WeakReferenceOwner(bool bound_to_current_sequence)
+    : bound_to_constructor_sequence_(bound_to_current_sequence) {
+  if (bound_to_current_sequence)
+    flag_ = new WeakReference::Flag(bound_to_current_sequence);
 }
 
 WeakReferenceOwner::~WeakReferenceOwner() {
@@ -50,9 +55,10 @@ WeakReferenceOwner::~WeakReferenceOwner() {
 }
 
 WeakReference WeakReferenceOwner::GetRef() const {
-  // If we hold the last reference to the Flag then create a new one.
-  if (!HasRefs())
-    flag_ = new WeakReference::Flag();
+  // If not bound to the constructor sequence, and there are no outstanding weak
+  // pointers, recreate flag to allow re-binding to a different sequence.
+  if (!bound_to_constructor_sequence_ && !HasRefs())
+    flag_ = new WeakReference::Flag(false /* bound_to_constructor_sequence_ */);
 
   return WeakReference(flag_.get());
 }