Bug 1819160 - Hold a reference to registering session in DocAccessibleParent. r=Jamie

This should fully eliminate the case where remote accessibles fail to
unregister because of the outer PresShell's lifecycle.

Differential Revision: https://phabricator.services.mozilla.com/D172473

accessible/android/SessionAccessibility.cpp

@@ -273,9 +273,12 @@ RefPtr<SessionAccessibility> SessionAccessibility::GetInstanceFor(
       return GetInstanceFor(doc->GetPresShell());
     }
   } else {
+    DocAccessibleParent* remoteDoc = aAccessible->AsRemote()->Document();
+    if (remoteDoc->mSessionAccessibility) {
+      return remoteDoc->mSessionAccessibility;
+    }
     dom::CanonicalBrowsingContext* cbc =
-        static_cast<dom::BrowserParent*>(
-            aAccessible->AsRemote()->Document()->Manager())
+        static_cast<dom::BrowserParent*>(remoteDoc->Manager())
             ->GetBrowsingContext()
             ->Top();
     dom::BrowserParent* bp = cbc->GetBrowserParent();
@@ -286,7 +289,10 @@ RefPtr<SessionAccessibility> SessionAccessibility::GetInstanceFor(
     if (auto element = bp->GetOwnerElement()) {
       if (auto doc = element->OwnerDoc()) {
         if (nsPresContext* presContext = doc->GetPresContext()) {
-          return GetInstanceFor(presContext->PresShell());
+          RefPtr<SessionAccessibility> sessionAcc =
+              GetInstanceFor(presContext->PresShell());
+          remoteDoc->mSessionAccessibility = sessionAcc;
+          return sessionAcc;
         }
       } else {
         MOZ_ASSERT_UNREACHABLE(
@@ -1080,6 +1086,7 @@ void SessionAccessibility::UnregisterAccessible(Accessible* aAccessible) {
   }
 
   RefPtr<SessionAccessibility> sessionAcc = GetInstanceFor(aAccessible);
+  MOZ_ASSERT(sessionAcc, "Need SessionAccessibility to unregister Accessible!");
   if (sessionAcc) {
     Accessible* registeredAcc =
         sessionAcc->mIDToAccessibleMap.Get(virtualViewID);

accessible/ipc/DocAccessibleParent.cpp

@@ -31,6 +31,7 @@
 #endif
 
 #if defined(ANDROID)
+#  include "mozilla/a11y/SessionAccessibility.h"
 #  define ACQUIRE_ANDROID_LOCK \
     MonitorAutoLock mal(nsAccessibilityService::GetAndroidMonitor());
 #else

accessible/ipc/DocAccessibleParent.h

@@ -29,6 +29,10 @@ class xpcAccessibleGeneric;
 class DocAccessiblePlatformExtParent;
 #endif
 
+#ifdef ANDROID
+class SessionAccessibility;
+#endif
+
 /*
  * These objects live in the main process and comunicate with and represent
  * an accessible document in a content process.
@@ -354,6 +358,10 @@ class DocAccessibleParent : public RemoteAccessible,
 
   size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) override;
 
+#ifdef ANDROID
+  RefPtr<SessionAccessibility> mSessionAccessibility;
+#endif
+
  private:
   ~DocAccessibleParent();
 

accessible/ipc/moz.build

@@ -27,6 +27,7 @@ else:
     elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "android":
         LOCAL_INCLUDES += [
             "/accessible/android",
+            "/widget/android",
         ]
     else:
         LOCAL_INCLUDES += [