Bug 1284350. Reland on top of backouts "Bug 1282710 - Part 1 - implement the suspend and resume logics in HTMLMediaElement.cpp according to visibility events; r=cpearce r=kamidphish" r=kaku

Instead of "not visible", "approximately visible", and "visible" (in display port) we now have "approximately not visible", and "approximately visible" which includes "visible".

dom/html/HTMLMediaElement.cpp

@@ -6017,6 +6017,48 @@ HTMLMediaElement::IsAllowedToPlay()
   return true;
 }
 
+static const char* VisibilityString(Visibility aVisibility) {
+  switch(aVisibility) {
+    case Visibility::UNTRACKED: {
+      return "UNTRACKED";
+    }
+    case Visibility::APPROXIMATELY_NONVISIBLE: {
+      return "APPROXIMATELY_NONVISIBLE";
+    }
+    case Visibility::APPROXIMATELY_VISIBLE: {
+      return "APPROXIMATELY_VISIBLE";
+    }
+  }
+
+  return "NAN";
+}
+
+void
+HTMLMediaElement::OnVisibilityChange(Visibility aNewVisibility)
+{
+  LOG(LogLevel::Debug, ("OnVisibilityChange(): %s\n",
+      VisibilityString(aNewVisibility)));
+
+  if (!mDecoder) {
+    return;
+  }
+
+  switch (aNewVisibility) {
+    case Visibility::UNTRACKED: {
+        MOZ_ASSERT_UNREACHABLE("Shouldn't notify for untracked visibility");
+        break;
+    }
+    case Visibility::APPROXIMATELY_NONVISIBLE: {
+      mDecoder->NotifyOwnerActivityChanged(false);
+      break;
+    }
+    case Visibility::APPROXIMATELY_VISIBLE: {
+      mDecoder->NotifyOwnerActivityChanged(true);
+      break;
+    }
+  }
+
+}
 #ifdef MOZ_EME
 MediaKeys*
 HTMLMediaElement::GetMediaKeys() const