Bug 1821963 part 5: Remove code to prevent handling of window messages while handling PDocAccessible sync IPDL calls. r=handyman

This actually hasn't ever been used in a shipping build of Firefox.
Although sync IPDL was tried with Windos a11y for a while when e10s was still disabled, it was never feasible and was replaced with COM proxying.

Differential Revision: https://phabricator.services.mozilla.com/D177965

dom/ipc/ContentParent.cpp

@@ -25,9 +25,6 @@
 #include "nsComponentManagerUtils.h"
 #include "nsIBrowserDOMWindow.h"
 
-#ifdef ACCESSIBILITY
-#  include "mozilla/a11y/PDocAccessible.h"
-#endif
 #include "GMPServiceParent.h"
 #include "HandlerServiceParent.h"
 #include "IHistory.h"
@@ -6245,22 +6242,6 @@ ContentParent::RecvUnstoreAndBroadcastBlobURLUnregistration(
   return IPC_OK();
 }
 
-bool ContentParent::HandleWindowsMessages(const Message& aMsg) const {
-  MOZ_ASSERT(aMsg.is_sync());
-
-#ifdef ACCESSIBILITY
-  // a11y messages can be triggered by windows messages, which means if we
-  // allow handling windows messages while we wait for the response to a sync
-  // a11y message we can reenter the ipc message sending code.
-  if (a11y::PDocAccessible::PDocAccessibleStart < aMsg.type() &&
-      a11y::PDocAccessible::PDocAccessibleEnd > aMsg.type()) {
-    return false;
-  }
-#endif
-
-  return true;
-}
-
 mozilla::ipc::IPCResult ContentParent::RecvGetFilesRequest(
     const nsID& aUUID, const nsAString& aDirectoryPath,
     const bool& aRecursiveFlag) {

dom/ipc/ContentParent.h

@@ -483,8 +483,6 @@ class ContentParent final : public PContentParent,
   bool DeallocPContentPermissionRequestParent(
       PContentPermissionRequestParent* actor);
 
-  virtual bool HandleWindowsMessages(const Message& aMsg) const override;
-
   void ForkNewProcess(bool aBlocking);
 
   mozilla::ipc::IPCResult RecvCreateWindow(

ipc/glue/MessageChannel.cpp

@@ -1312,7 +1312,6 @@ bool MessageChannel::Send(UniquePtr<Message> aMsg, UniquePtr<Message>* aReply) {
   int32_t transaction = nest ? stackTop->TransactionID() : seqno;
   aMsg->set_transaction_id(transaction);
 
-  bool handleWindowsMessages = mListener->HandleWindowsMessages(*aMsg.get());
   AutoEnterTransaction transact(this, seqno, transaction, nestedLevel);
 
   IPC_LOG("Send seqno=%d, xid=%d", seqno, transaction);
@@ -1340,7 +1339,7 @@ bool MessageChannel::Send(UniquePtr<Message> aMsg, UniquePtr<Message>* aReply) {
     MOZ_RELEASE_ASSERT(!transact.IsComplete());
     MOZ_RELEASE_ASSERT(mTransactionStack == &transact);
 
-    bool maybeTimedOut = !WaitForSyncNotify(handleWindowsMessages);
+    bool maybeTimedOut = !WaitForSyncNotify();
 
     if (mListener->NeedArtificialSleep()) {
       MonitorAutoUnlock unlock(*mMonitor);
@@ -1828,7 +1827,7 @@ bool MessageChannel::WaitResponse(bool aWaitTimedOut) {
 }
 
 #ifndef OS_WIN
-bool MessageChannel::WaitForSyncNotify(bool /* aHandleWindowsMessages */) {
+bool MessageChannel::WaitForSyncNotify() {
   AssertWorkerThread();
 #  ifdef DEBUG
   // WARNING: We don't release the lock here. We can't because the link

ipc/glue/MessageChannel.h

@@ -405,7 +405,7 @@ class MessageChannel : HasResultCodes {
   //
   // So in sum: true is a meaningful return value; false isn't,
   // necessarily.
-  bool WaitForSyncNotify(bool aHandleWindowsMessages) MOZ_REQUIRES(*mMonitor);
+  bool WaitForSyncNotify() MOZ_REQUIRES(*mMonitor);
 
   bool WaitResponse(bool aWaitTimedOut);
 

ipc/glue/ProtocolUtils.h

@@ -470,12 +470,6 @@ class IToplevelProtocol : public IProtocol {
 
   bool IsOnCxxStack() const;
 
-  /**
-   * Return true if windows messages can be handled while waiting for a reply
-   * to a sync IPDL message.
-   */
-  virtual bool HandleWindowsMessages(const Message& aMsg) const { return true; }
-
   virtual void ProcessRemoteNativeEventsInInterruptCall() {}
 
   virtual void OnChannelReceivedMessage(const Message& aMsg) {}

ipc/glue/WindowsMessageLoop.cpp

@@ -850,7 +850,7 @@ SuppressedNeuteringRegion::~SuppressedNeuteringRegion() {
 
 bool SuppressedNeuteringRegion::sSuppressNeutering = false;
 
-bool MessageChannel::WaitForSyncNotify(bool aHandleWindowsMessages) {
+bool MessageChannel::WaitForSyncNotify() {
   mMonitor->AssertCurrentThreadOwns();
 
   if (!gUIThreadId) {
@@ -859,8 +859,7 @@ bool MessageChannel::WaitForSyncNotify(bool aHandleWindowsMessages) {
 
   // Use a blocking wait if this channel does not require
   // Windows message deferral behavior.
-  if (!(mFlags & REQUIRE_DEFERRED_MESSAGE_PROTECTION) ||
-      !aHandleWindowsMessages) {
+  if (!(mFlags & REQUIRE_DEFERRED_MESSAGE_PROTECTION)) {
     TimeDuration timeout = (kNoTimeout == mTimeoutMs)
                                ? TimeDuration::Forever()
                                : TimeDuration::FromMilliseconds(mTimeoutMs);