Bug 1296531 - Add MediaSegment::IsNull. r=jesup

This allows us to see if all chunks in a MediaSegment are null.
When this is true for the MediaSegment passed to NotifyQueuedChanges, we can
assume that the track's input is blocked for the given time.

MozReview-Commit-ID: zf7V7aiohg

--HG--
extra : rebase_source : 5dd8442f85e6011fc0015460c6a7fedf04fb956e

dom/media/AudioSegment.h

@@ -408,16 +408,6 @@ public:
     return 0;
   }
 
-  bool IsNull() const {
-    for (ChunkIterator ci(*const_cast<AudioSegment*>(this)); !ci.IsEnded();
-         ci.Next()) {
-      if (!ci->IsNull()) {
-        return false;
-      }
-    }
-    return true;
-  }
-
   static Type StaticType() { return AUDIO; }
 
   size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const override

dom/media/MediaSegment.h

@@ -148,6 +148,11 @@ public:
     mLastPrincipalHandle = aLastPrincipalHandle;
   }
 
+  /**
+   * Returns true if all chunks in this segment are null.
+   */
+  virtual bool IsNull() const = 0;
+
   /**
    * Create a MediaSegment of the same type.
    */
@@ -229,6 +234,15 @@ protected:
  */
 template <class C, class Chunk> class MediaSegmentBase : public MediaSegment {
 public:
+  bool IsNull() const override
+  {
+    for (typename C::ConstChunkIterator iter(*this); !iter.IsEnded(); iter.Next()) {
+      if (!iter->IsNull()) {
+        return false;
+      }
+    }
+    return true;
+  }
   MediaSegment* CreateEmptyClone() const override
   {
     return new C();