Bug 1543313 part 1: Allow identification and retrieval of DocAccessibleParents at the top level of their content process. r=eeejay

DocAccessibleParent already has IsTopLevel(), which identifies a document at the top level of the hierarchy; i.e. it has no parents.
Now that we have out-of-process iframes, we need to be able to identify and retrieve documents at the top level of their content process, even if they are embedded by another remote document.
DocAccessibleParent::IsTopLevelInContentProcess() has been introduced to achieve this.
BrowserParent::GetTopLevelDocAccessible() now uses this instead of IsTopLevel(), since we want to be able to get the top DocAccessibleParent even for a BrowserParent for an out-of-process iframe.

Differential Revision: https://phabricator.services.mozilla.com/D32282

--HG--
extra : moz-landing-system : lando

accessible/ipc/DocAccessibleParent.h

@@ -36,6 +36,7 @@ class DocAccessibleParent : public ProxyAccessible,
         mEmulatedWindowHandle(nullptr),
 #endif  // defined(XP_WIN)
         mTopLevel(false),
+        mTopLevelInContentProcess(false),
         mShutdown(false) {
     sMaxDocID++;
     mActorID = sMaxDocID;
@@ -43,9 +44,27 @@ class DocAccessibleParent : public ProxyAccessible,
     LiveDocs().Put(mActorID, this);
   }
 
-  void SetTopLevel() { mTopLevel = true; }
+  /**
+   * Set this as a top level document; i.e. it is not embedded by another remote
+   * document. This also means it is a top level document in its content
+   * process.
+   * Tab documents are top level documents.
+   */
+  void SetTopLevel() {
+    mTopLevel = true;
+    mTopLevelInContentProcess = true;
+  }
   bool IsTopLevel() const { return mTopLevel; }
 
+  /**
+   * Set this as a top level document in its content process.
+   * Note that this could be an out-of-process iframe embedded by a remote
+   * embedder document. In that case, IsToplevel() will return false, but
+   * IsTopLevelInContentProcess() will return true.
+   */
+  void SetTopLevelInContentProcess() { mTopLevelInContentProcess = true; }
+  bool IsTopLevelInContentProcess() const { return mTopLevelInContentProcess; }
+
   bool IsShutdown() const { return mShutdown; }
 
   /**
@@ -279,6 +298,7 @@ class DocAccessibleParent : public ProxyAccessible,
   nsTHashtable<ProxyEntry> mAccessibles;
   uint64_t mActorID;
   bool mTopLevel;
+  bool mTopLevelInContentProcess;
   bool mShutdown;
 
   static uint64_t sMaxDocID;

dom/ipc/BrowserParent.cpp

@@ -409,7 +409,11 @@ a11y::DocAccessibleParent* BrowserParent::GetTopLevelDocAccessible() const {
       ManagedPDocAccessibleParent();
   for (auto iter = docs.ConstIter(); !iter.Done(); iter.Next()) {
     auto doc = static_cast<a11y::DocAccessibleParent*>(iter.Get()->GetKey());
-    if (doc->IsTopLevel()) {
+    // We want the document for this BrowserParent even if it's for an
+    // embedded out-of-process iframe. Therefore, we use
+    // IsTopLevelInContentProcess. In contrast, using IsToplevel would only
+    // include documents that aren't embedded; e.g. tab documents.
+    if (doc->IsTopLevelInContentProcess()) {
       return doc;
     }
   }
@@ -1122,6 +1126,7 @@ mozilla::ipc::IPCResult BrowserParent::RecvPDocAccessibleConstructor(
     // In this case, we don't get aParentDoc and aParentID.
     MOZ_ASSERT(!aParentDoc && !aParentID);
     MOZ_ASSERT(embedderID);
+    doc->SetTopLevelInContentProcess();
 #  ifdef XP_WIN
     MOZ_ASSERT(!aDocCOMProxy.IsNull());
     RefPtr<IAccessible> proxy(aDocCOMProxy.Get());

dom/ipc/BrowserParent.h

@@ -162,7 +162,12 @@ class BrowserParent final : public PBrowserParent,
   nsIXULBrowserWindow* GetXULBrowserWindow();
 
   /**
-   * Return the top level doc accessible parent for this tab.
+   * Return the top level DocAccessibleParent for this BrowserParent.
+   * Note that in the case of an out-of-process iframe, the returned actor
+   * might not be at the top level of the DocAccessibleParent tree; i.e. it
+   * might have a parent. However, it will be at the top level in its content
+   * process. That is, doc->IsTopLevelInContentProcess() will always be true,
+   * but doc->IsTopLevel() might not.
    */
   a11y::DocAccessibleParent* GetTopLevelDocAccessible() const;