Change return types of refcount methods.

AddRef() now returns void, and Release() returns an enum
RefCountReleaseStatus, to indicate whether or not this Release
call implied deletion.

Bug: webrtc:8270
Change-Id: If2fb77f26118b61751b51c856af187c72112c630
Reviewed-on: https://webrtc-review.googlesource.com/3320
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20366}

rtc_base/callback_unittest.cc

@@ -31,11 +31,11 @@ struct BindTester {
 class RefCountedBindTester : public RefCountInterface {
  public:
   RefCountedBindTester() : count_(0) {}
-  int AddRef() const override {
-    return ++count_;
-  }
-  int Release() const override {
-    return --count_;
+  void AddRef() const override { ++count_; }
+  RefCountReleaseStatus Release() const override {
+    --count_;
+    return count_ == 0 ? RefCountReleaseStatus::kDroppedLastRef
+                       : RefCountReleaseStatus::kOtherRefsRemained;
   }
   int RefCount() const { return count_; }