Add multiple destruction callbacks to AndroidOverlay.

media/base/android/android_overlay.cc

Index: media/base/android/android_overlay.cc
diff --git a/media/base/android/android_overlay.cc b/media/base/android/android_overlay.cc
index 53fe296681f1ad9d422591c8f72994e3433aefc7..a50adc99a9fc6d7eef3d4361a31d78acacd5fef3 100644
--- a/media/base/android/android_overlay.cc
+++ b/media/base/android/android_overlay.cc
@@ -6,4 +6,32 @@
 
 namespace media {
 
+AndroidOverlay::AndroidOverlay() : weak_factory_(this) {}
+AndroidOverlay::~AndroidOverlay() {}
+
+void AndroidOverlay::AddDestructionCallback(
+    AndroidOverlayConfig::DestroyedCB cb) {
+  destruction_cbs_.push_back(std::move(cb));
+}
+
+void AndroidOverlay::RunDestructionCallbacks() {
+  if (!destruction_cbs_.size())

[watk, 2017/05/16 19:10:28]

nit: More idiomatic to write .empty() I think

[liberato (no reviews please), 2017/05/16 20:04:02]

Done.

+    return;
+
+  // Move the list, in case it's modified during traversal.
+  std::list<AndroidOverlayConfig::DestroyedCB> cbs =
+      std::move(destruction_cbs_);
+
+  // Get a wp for |this|, in case it's destroyed during a callback.
+  base::WeakPtr<AndroidOverlay> wp = weak_factory_.GetWeakPtr();
+
+  for (auto& cb : cbs) {
+    std::move(cb).Run(this);
+    // If |this| has been deleted, then stop here.  We don't want to call back
+    // with an invalid |this| ptr.

[watk, 2017/05/16 19:10:28]

nit: not sure I understand the rationale as written. Doesn't seem to be a
problem if |this| is deleted. i.e., it's conceivable that we would keep running
cbs.

IMO the reason is just that we provide the reasonable contract that
destruction_cbs will not be called after the overlay is deleted.

[liberato (no reviews please), 2017/05/16 20:04:02]

if we call with |this| after it's deleted, then it's unclear what the caller
would do with it.  it might be aliased to some other overlay by that point.

i'll just shorted the comment to the first sentence, and avoid the issue :)

+    if (!wp)
+      return;
+  }
+}
+
 }  // namespace media