Bug 1470430 - MediaDocumentStreamListener should allow off main thread OnDataAvailable calls. r=smaug

This patch makes MediaDocumentStreamListener implement the
nsIThreadRetargetableStreamListener interface. This allows callers to
redirect the OnDataAvailable calls to another thread if possible. Since
ImageDocument's use ImageListener which inherits from this class, and we
are often viewing large images this way, it would be nice to move the IO
to the image IO thread.

dom/html/MediaDocument.cpp

@@ -23,23 +23,30 @@
 #include "nsServiceManagerUtils.h"
 #include "nsIPrincipal.h"
 #include "nsIMultiPartChannel.h"
+#include "nsProxyRelease.h"
 
 namespace mozilla {
 namespace dom {
 
 MediaDocumentStreamListener::MediaDocumentStreamListener(MediaDocument *aDocument)
+  : mDocument(aDocument)
 {
-  mDocument = aDocument;
 }
 
 MediaDocumentStreamListener::~MediaDocumentStreamListener()
 {
+  if (mDocument && !NS_IsMainThread()) {
+    nsCOMPtr<nsIEventTarget> mainTarget(do_GetMainThread());
+    NS_ProxyRelease("MediaDocumentStreamListener::mDocument",
+                    mainTarget, mDocument.forget());
+  }
 }
 
 
 NS_IMPL_ISUPPORTS(MediaDocumentStreamListener,
                   nsIRequestObserver,
-                  nsIStreamListener)
+                  nsIStreamListener,
+                  nsIThreadRetargetableStreamListener)
 
 
 void
@@ -99,6 +106,17 @@ MediaDocumentStreamListener::OnDataAvailable(nsIRequest* request,
   return NS_OK;
 }
 
+NS_IMETHODIMP
+MediaDocumentStreamListener::CheckListenerChain()
+{
+  nsCOMPtr<nsIThreadRetargetableStreamListener> retargetable =
+    do_QueryInterface(mNextStream);
+  if (retargetable) {
+    return retargetable->CheckListenerChain();
+  }
+  return NS_ERROR_NO_INTERFACE;
+}
+
 // default format names for MediaDocument.
 const char* const MediaDocument::sFormatNames[4] =
 {

dom/html/MediaDocument.h

@@ -11,6 +11,7 @@
 #include "nsHTMLDocument.h"
 #include "nsGenericHTMLElement.h"
 #include "nsIStringBundle.h"
+#include "nsIThreadRetargetableStreamListener.h"
 
 #define NSMEDIADOCUMENT_PROPERTIES_URI "chrome://global/locale/layout/MediaDocument.properties"
 
@@ -92,7 +93,9 @@ private:
 };
 
 
-class MediaDocumentStreamListener: public nsIStreamListener
+class MediaDocumentStreamListener
+  : public nsIStreamListener
+  , public nsIThreadRetargetableStreamListener
 {
 protected:
   virtual ~MediaDocumentStreamListener();
@@ -101,12 +104,14 @@ public:
   explicit MediaDocumentStreamListener(MediaDocument* aDocument);
   void SetStreamListener(nsIStreamListener *aListener);
 
-  NS_DECL_ISUPPORTS
+  NS_DECL_THREADSAFE_ISUPPORTS
 
   NS_DECL_NSIREQUESTOBSERVER
 
   NS_DECL_NSISTREAMLISTENER
 
+  NS_DECL_NSITHREADRETARGETABLESTREAMLISTENER
+
   void DropDocumentRef()
   {
     mDocument = nullptr;