Add multiple destruction callbacks to AndroidOverlay.

media/base/android/android_overlay.cc

 // Copyright 2017 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 "media/base/android/android_overlay.h"
 
 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