Bug 1415478 - part2 : allow autoplay for non-audible media content and video without audio content. r=jwwang

Per UX spec, we would allow non-audible media (volume 0, muted, video without audio track)
to autoplay.

MozReview-Commit-ID: HKUyt5Jt4sH

--HG--
extra : rebase_source : fa8d1bfd2fb667e974dbe499d7f8215273d4fa10

dom/html/HTMLMediaElement.cpp

@@ -670,11 +670,6 @@ void HTMLMediaElement::ReportLoadError(const char* aMsg,
                                   aParamCount);
 }
 
-static bool IsAutoplayEnabled()
-{
-  return Preferences::GetBool("media.autoplay.enabled");
-}
-
 class HTMLMediaElement::AudioChannelAgentCallback final :
   public nsIAudioChannelAgentCallback
 {
@@ -2434,7 +2429,8 @@ void HTMLMediaElement::UpdatePreloadAction()
   PreloadAction nextAction = PRELOAD_UNDEFINED;
   // If autoplay is set, or we're playing, we should always preload data,
   // as we'll need it to play.
-  if ((IsAutoplayEnabled() && HasAttr(kNameSpaceID_None, nsGkAtoms::autoplay)) ||
+  if ((AutoplayPolicy::IsMediaElementAllowedToPlay(WrapNotNull(this)) &&
+       HasAttr(kNameSpaceID_None, nsGkAtoms::autoplay)) ||
       !mPaused)
   {
     nextAction = HTMLMediaElement::PRELOAD_ENOUGH;
@@ -6178,7 +6174,7 @@ bool HTMLMediaElement::CanActivateAutoplay()
   // download is controlled by the script and there is no way to evaluate
   // MediaDecoder::CanPlayThrough().
 
-  if (!IsAutoplayEnabled()) {
+  if (!AutoplayPolicy::IsMediaElementAllowedToPlay(WrapNotNull(this))) {
     return false;
   }
 

dom/media/AutoplayPolicy.cpp

@@ -7,7 +7,6 @@
 #include "AutoplayPolicy.h"
 
 #include "mozilla/EventStateManager.h"
-#include "mozilla/NotNull.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/dom/HTMLMediaElement.h"
 #include "nsIDocument.h"
@@ -18,10 +17,6 @@ namespace dom {
 /* static */ bool
 AutoplayPolicy::IsDocumentAllowedToPlay(nsIDocument* aDoc)
 {
-  if (!Preferences::GetBool("media.autoplay.enabled.user-gestures-needed")) {
-    return true;
-  }
-
   return aDoc ? aDoc->HasBeenUserActivated() : false;
 }
 
@@ -32,13 +27,25 @@ AutoplayPolicy::IsMediaElementAllowedToPlay(NotNull<HTMLMediaElement*> aElement)
     return true;
   }
 
-  if (Preferences::GetBool("media.autoplay.enabled.user-gestures-needed", false)) {
-    return AutoplayPolicy::IsDocumentAllowedToPlay(aElement->OwnerDoc());
-  }
-
   // TODO : this old way would be removed when user-gestures-needed becomes
   // as a default option to block autoplay.
+  if (!Preferences::GetBool("media.autoplay.enabled.user-gestures-needed", false)) {
     return EventStateManager::IsHandlingUserInput();
+   }
+
+  // Muted content
+  if (aElement->Volume() == 0.0 || aElement->Muted()) {
+    return true;
+  }
+
+  // Media has already loaded metadata and doesn't contain audio track
+  if (aElement->IsVideo() &&
+      aElement->ReadyState() >= nsIDOMHTMLMediaElement::HAVE_METADATA &&
+      !aElement->HasAudio()) {
+    return true;
+  }
+
+  return AutoplayPolicy::IsDocumentAllowedToPlay(aElement->OwnerDoc());
 }
 
 } // namespace dom

dom/media/AutoplayPolicy.h

@@ -25,13 +25,14 @@ class HTMLMediaElement;
  * conditions is true.
  * 1) Owner document is activated by user gestures
  *    We restrict user gestures to "mouse click", "keyboard press" and "touch".
- * 2) TODO...
+ * 2) Muted media content or video without audio content
  */
 class AutoplayPolicy
 {
 public:
-  static bool IsDocumentAllowedToPlay(nsIDocument* aDoc);
   static bool IsMediaElementAllowedToPlay(NotNull<HTMLMediaElement*> aElement);
+private:
+  static bool IsDocumentAllowedToPlay(nsIDocument* aDoc);
 };
 
 } // namespace dom