Fix WeakPtrFactory members in Android media classes

This forces WeakPtrs to be invalidated before other members' destructors run.
See the bug or the documentation of WeakPtrFactory for more information. I'm
in the process of trying to turn on a clang check for this (see the bug).

BUG=303818
TBR=qinmin@chromium.org

Review URL: https://codereview.chromium.org/841453006

Cr-Commit-Position: refs/heads/master@{#311506}

content/renderer/media/android/media_source_delegate.cc

@@ -65,8 +65,8 @@ MediaSourceDelegate::MediaSourceDelegate(
       main_task_runner_(base::MessageLoopProxy::current()),
       media_task_runner_(media_task_runner),
       main_weak_factory_(this),
-      media_weak_factory_(this),
-      main_weak_this_(main_weak_factory_.GetWeakPtr()) {
+      media_weak_factory_(this) {
+  main_weak_this_ = main_weak_factory_.GetWeakPtr();
   DCHECK(main_task_runner_->BelongsToCurrentThread());
 }
 

content/renderer/media/android/media_source_delegate.h

@@ -227,9 +227,9 @@ class MediaSourceDelegate : public media::DemuxerHost {
   const scoped_refptr<base::SingleThreadTaskRunner> media_task_runner_;
 
   // NOTE: Weak pointers must be invalidated before all other member variables.
+  base::WeakPtr<MediaSourceDelegate> main_weak_this_;
   base::WeakPtrFactory<MediaSourceDelegate> main_weak_factory_;
   base::WeakPtrFactory<MediaSourceDelegate> media_weak_factory_;
-  base::WeakPtr<MediaSourceDelegate> main_weak_this_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaSourceDelegate);
 };

media/base/android/media_source_player.h

@@ -273,9 +273,9 @@ class MEDIA_EXPORT MediaSourcePlayer : public MediaPlayerAndroid,
   bool prerolling_;
 
   // Weak pointer passed to media decoder jobs for callbacks.
+  base::WeakPtr<MediaSourcePlayer> weak_this_;
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<MediaSourcePlayer> weak_factory_;
-  base::WeakPtr<MediaSourcePlayer> weak_this_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaSourcePlayer);
 };