Bug 1440195 Add a random context seed for AudioContext and MediaStream r=baku

MozReview-Commit-ID: sHpVCgd8Fs

--HG--
extra : rebase_source : e1bbeab189b7a64c4ce051b74bc19a706b0fa1e8

dom/media/DOMMediaStream.cpp

@@ -572,8 +572,12 @@ DOMMediaStream::CurrentTime()
   if (!mPlaybackStream) {
     return 0.0;
   }
+  // The value of a MediaStream's CurrentTime will always advance forward; it will never
+  // reset (even if one rewinds a video.) Therefore we can use a single Random Seed
+  // initialized at the same time as the object.
   return nsRFPService::ReduceTimePrecisionAsSecs(mPlaybackStream->
-    StreamTimeToSeconds(mPlaybackStream->GetCurrentTime() - mLogicalStreamStartTime));
+    StreamTimeToSeconds(mPlaybackStream->GetCurrentTime() - mLogicalStreamStartTime),
+    GetRandomTimelineSeed());
 }
 
 already_AddRefed<Promise>

dom/media/DOMMediaStream.h

@@ -16,6 +16,7 @@
 #include "nsIPrincipal.h"
 #include "MediaTrackConstraints.h"
 #include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/RelativeTimeline.h"
 #include "PrincipalChangeObserver.h"
 
 // X11 has a #define for CurrentTime. Unbelievable :-(.
@@ -202,7 +203,8 @@ protected:
  *                                                     (pointing to t2 in A')
  */
 class DOMMediaStream : public DOMEventTargetHelper,
-                       public dom::PrincipalChangeObserver<dom::MediaStreamTrack>
+                       public dom::PrincipalChangeObserver<dom::MediaStreamTrack>,
+                       public RelativeTimeline
 {
   friend class DOMLocalMediaStream;
   friend class dom::MediaStreamTrack;

dom/media/webaudio/AudioContext.cpp

@@ -650,11 +650,15 @@ AudioContext::DestinationStream() const
 }
 
 double
-AudioContext::CurrentTime() const
+AudioContext::CurrentTime()
 {
   MediaStream* stream = Destination()->Stream();
+  // The value of a MediaStream's CurrentTime will always advance forward; it will never
+  // reset (even if one rewinds a video.) Therefore we can use a single Random Seed
+  // initialized at the same time as the object.
   return nsRFPService::ReduceTimePrecisionAsSecs(
-    stream->StreamTimeToSeconds(stream->GetCurrentTime()));
+    stream->StreamTimeToSeconds(stream->GetCurrentTime()),
+    GetRandomTimelineSeed());
 }
 
 void AudioContext::DisconnectFromOwner()

dom/media/webaudio/AudioContext.h

@@ -13,6 +13,7 @@
 #include "mozilla/DOMEventTargetHelper.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/dom/TypedArray.h"
+#include "mozilla/RelativeTimeline.h"
 #include "mozilla/UniquePtr.h"
 #include "nsCOMPtr.h"
 #include "nsCycleCollectionParticipant.h"
@@ -117,7 +118,8 @@ private:
 enum class AudioContextOperation { Suspend, Resume, Close };
 
 class AudioContext final : public DOMEventTargetHelper,
-                           public nsIMemoryReporter
+                           public nsIMemoryReporter,
+                           public RelativeTimeline
 {
   AudioContext(nsPIDOMWindowInner* aParentWindow,
                bool aIsOffline,
@@ -181,7 +183,7 @@ public:
 
   bool ShouldSuspendNewStream() const { return mSuspendCalled; }
 
-  double CurrentTime() const;
+  double CurrentTime();
 
   AudioListener* Listener();