Issue #2736 - Part 8: Re-work <video> and <audio> src attribute.

Use subject principal as triggering principal in <video>/<audio> "src"
attribute. We deviate from Mozilla here because we do not worry
about content isolation principals in Page Info.

dom/html/HTMLMediaElement.cpp

@@ -3734,6 +3734,9 @@ HTMLMediaElement::AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aName,
   if (aNameSpaceID == kNameSpaceID_None) {
     if (aName == nsGkAtoms::src) {
       mSrcMediaSource = nullptr;
+      mSrcAttrTriggeringPrincipal = nsContentUtils::GetAttrTriggeringPrincipal(
+          this, aValue ? aValue->GetStringValue() : EmptyString(),
+          aMaybeScriptedPrincipal);
       if (aValue) {
         nsString srcStr = aValue->GetStringValue();
         nsCOMPtr<nsIURI> uri;

dom/html/HTMLMediaElement.h

@@ -410,10 +410,13 @@ public:
 
   MediaError* GetError() const;
 
-  // XPCOM GetSrc() is OK
-  void SetSrc(const nsAString& aSrc, ErrorResult& aRv)
+  void GetSrc(nsString& aSrc, nsIPrincipal&)
   {
-    SetHTMLAttr(nsGkAtoms::src, aSrc, aRv);
+    GetSrc(aSrc); // XPCOM
+  }
+  void SetSrc(const nsAString& aSrc, nsIPrincipal& aTriggeringPrincipal, ErrorResult& aRv)
+  {
+    SetHTMLAttr(nsGkAtoms::src, aSrc, aTriggeringPrincipal, aRv);
   }
 
   // XPCOM GetCurrentSrc() is OK
@@ -1326,6 +1329,9 @@ protected:
   // set in the src attribute.
   RefPtr<DOMMediaStream> mSrcAttrStream;
 
+  // Holds the triggering principal for the src attribute.
+  nsCOMPtr<nsIPrincipal> mSrcAttrTriggeringPrincipal;
+
   // Holds a reference to the DOM wrapper for the MediaStream that we're
   // actually playing.
   // At most one of mDecoder and mSrcStream can be non-null.

dom/webidl/HTMLMediaElement.webidl

@@ -17,7 +17,7 @@ interface HTMLMediaElement : HTMLElement {
   readonly attribute MediaError? error;
 
   // network state
-  [CEReactions, SetterThrows]
+  [CEReactions, NeedsSubjectPrincipal, SetterThrows]
            attribute DOMString src;
   readonly attribute DOMString currentSrc;