Bug 1572798 - Make content browsing contexts for tabs start as inactive. r=nika

Otherwise autoplay blocking until-in-foreground breaks with the other
patch in this bug, because it unblocks media playback once a browsing
context is active for the first time.

Differential Revision: https://phabricator.services.mozilla.com/D42329

browser/base/content/tabbrowser.js

@@ -2000,6 +2000,7 @@
       uriIsAboutBlank,
       userContextId,
       skipLoad,
+      initiallyActive,
     } = {}) {
       let b = document.createXULElement("browser");
       // Use the JSM global to create the permanentKey, so that if the
@@ -2032,6 +2033,10 @@
         b.setAttribute(attribute, defaultBrowserAttributes[attribute]);
       }
 
+      if (!initiallyActive) {
+        b.setAttribute("initiallyactive", "false");
+      }
+
       if (userContextId) {
         b.setAttribute("usercontextid", userContextId);
       }

docshell/base/BrowsingContext.cpp

@@ -344,8 +344,19 @@ already_AddRefed<BrowsingContext> BrowsingContext::CreateDetached(
   }
 
   nsContentUtils::GenerateUUIDInPlace(fields.mHistoryID);
-  fields.mExplicitActive =
-      parentBC ? ExplicitActiveStatus::None : ExplicitActiveStatus::Active;
+  fields.mExplicitActive = [&] {
+    if (parentBC) {
+      // Non-root browsing-contexts inherit their status from its parent.
+      return ExplicitActiveStatus::None;
+    }
+    if (aType == Type::Content) {
+      // Content gets managed by the chrome front-end / embedder element and
+      // starts as inactive.
+      return ExplicitActiveStatus::Inactive;
+    }
+    // Chrome starts as active.
+    return ExplicitActiveStatus::Active;
+  }();
 
   fields.mFullZoom = parentBC ? parentBC->FullZoom() : 1.0f;
   fields.mTextZoom = parentBC ? parentBC->TextZoom() : 1.0f;
@@ -633,8 +644,12 @@ void BrowsingContext::SetEmbedderElement(Element* aEmbedder) {
     if (XRE_IsParentProcess() && IsTopContent()) {
       nsAutoString messageManagerGroup;
       if (aEmbedder->IsXULElement()) {
-        aEmbedder->GetAttr(kNameSpaceID_None, nsGkAtoms::messagemanagergroup,
-                           messageManagerGroup);
+        aEmbedder->GetAttr(nsGkAtoms::messagemanagergroup, messageManagerGroup);
+        if (!aEmbedder->AttrValueIs(kNameSpaceID_None,
+                                    nsGkAtoms::initiallyactive,
+                                    nsGkAtoms::_false, eIgnoreCase)) {
+          txn.SetExplicitActive(ExplicitActiveStatus::Active);
+        }
       }
       txn.SetMessageManagerGroup(messageManagerGroup);
 

toolkit/components/printing/content/printUtils.js

@@ -156,6 +156,7 @@ var PrintUtils = {
         userContextId: browsingContext.originAttributes.userContextId,
         initialBrowsingContextGroupId: browsingContext.group.id,
         skipLoad: true,
+        initiallyActive: true,
       });
       browser.addEventListener("DOMWindowClose", function(e) {
         // Ignore close events from printing, see the code creating browsers in

xpcom/ds/StaticAtoms.py

@@ -2218,6 +2218,7 @@ STATIC_ATOMS = [
     Atom("forcemessagemanager", "forcemessagemanager"),
     Atom("preloadedState", "preloadedState"),
     Atom("initialBrowsingContextGroupId", "initialBrowsingContextGroupId"),
+    Atom("initiallyactive", "initiallyactive"),
     # windows media query names
     Atom("windows_win7", "windows-win7"),
     Atom("windows_win8", "windows-win8"),