Bug 1353030: document use of WrapRunnable(this) r=cpearce

MozReview-Commit-ID: Fb3KjsI9tE3

dom/media/gmp/GMPServiceParent.cpp

@@ -273,7 +273,11 @@ GeckoMediaPluginServiceParent::Observe(nsISupports* aSubject,
           gmpThread = mGMPThread;
         }
         if (gmpThread) {
-          gmpThread->Dispatch(WrapRunnable(this,
+          // Note: the GeckoMediaPluginServiceParent singleton is kept alive by a
+          // static refptr that is only cleared in the final stage of
+          // shutdown after everything else is shutdown, so this RefPtr<> is not
+          // strictly necessary so long as that is true, but it's safer.
+          gmpThread->Dispatch(WrapRunnable(RefPtr<GeckoMediaPluginServiceParent>(this),
                                            &GeckoMediaPluginServiceParent::CrashPlugins),
                               NS_DISPATCH_NORMAL);
         }

media/webrtc/signaling/src/media-conduit/WebrtcGmpVideoCodec.cpp

@@ -309,6 +309,7 @@ WebrtcGmpVideoEncoder::Encode(const webrtc::VideoFrame& aInputImage,
   MOZ_ASSERT(aInputImage.width() >= 0 && aInputImage.height() >= 0);
   // Would be really nice to avoid this sync dispatch, but it would require a
   // copy of the frame, since it doesn't appear to actually have a refcount.
+  // Passing 'this' is safe since this is synchronous.
   mGMPThread->Dispatch(
       WrapRunnable(this,
                    &WebrtcGmpVideoEncoder::Encode_g,
@@ -776,6 +777,7 @@ WebrtcGmpVideoDecoder::Decode(const webrtc::EncodedImage& aInputImage,
   MOZ_ASSERT(!NS_IsMainThread());
   // Would be really nice to avoid this sync dispatch, but it would require a
   // copy of the frame, since it doesn't appear to actually have a refcount.
+  // Passing 'this' is safe since this is synchronous.
   mozilla::SyncRunnable::DispatchToThread(mGMPThread,
                 WrapRunnableRet(&ret, this,
                                 &WebrtcGmpVideoDecoder::Decode_g,

media/webrtc/signaling/src/peerconnection/PeerConnectionMedia.cpp

@@ -1137,6 +1137,7 @@ PeerConnectionMedia::ShutdownMediaTransport_s()
 
   mIceCtxHdlr = nullptr;
 
+  // we're holding a ref to 'this' that's released by SelfDestruct_m
   mMainThread->Dispatch(WrapRunnable(this, &PeerConnectionMedia::SelfDestruct_m),
                         NS_DISPATCH_NORMAL);
 }

media/webrtc/signaling/src/peerconnection/WebrtcGlobalInformation.cpp

@@ -873,6 +873,8 @@ WebrtcGlobalChild::RecvGetLogRequest(const int& aRequestId,
     do_GetService(NS_SOCKETTRANSPORTSERVICE_CONTRACTID, &rv);
 
   if (NS_SUCCEEDED(rv) && stsThread) {
+    // this is a singleton, so we shouldn't need to hold a ref for the
+    // request (and can't just add a ref here anyways)
     rv = RUN_ON_THREAD(stsThread,
                        WrapRunnableNM(&GetLogging_s, this, aRequestId, aPattern.get()),
                        NS_DISPATCH_NORMAL);