Bug 1518002 - Update selection cache when initializing editor. r=masayuki

GitLab's comment calls scrollTop on input event handler. The scollTop may cause
reflow.  When causing reflow, editor is destroyed and initialized again. Then
nsTextEditorState will set current value to editor.  But this is failure.

By bug 1465702, selection is cached in edit action. When initializing editor,
selection controller is updated, so selection into cache becomes invalid. It
means that all selection methods will return error since document is different.

So we should update selection cache when initializing editor.

Also, I cannot create test case for this situation since we have to cause reflow
in input and/or composition event. Do you have any idea?

Differential Revision: https://phabricator.services.mozilla.com/D16944

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

editor/libeditor/EditorBase.cpp

@@ -263,6 +263,19 @@ nsresult EditorBase::Init(Document& aDocument, Element* aRoot,
   MOZ_ASSERT(selectionController,
              "Selection controller should be available at this point");
 
+  if (mEditActionData) {
+    // During edit action, selection is cached. But this selection is invalid
+    // now since selection controller is updated, so we have to update this
+    // cache.
+    Selection* selection = selectionController->GetSelection(
+        nsISelectionController::SELECTION_NORMAL);
+    NS_WARNING_ASSERTION(selection,
+                         "We cannot update selection cache in the edit action");
+    if (selection) {
+      mEditActionData->UpdateSelectionCache(*selection);
+    }
+  }
+
   // set up root element if we are passed one.
   if (aRoot) {
     mRootElement = aRoot;

editor/libeditor/EditorBase.h

@@ -732,6 +732,16 @@ class EditorBase : public nsIEditor,
       return mParentData ? mParentData->RangeUpdaterRef() : mRangeUpdater;
     }
 
+    void UpdateSelectionCache(Selection& aSelection) {
+      AutoEditActionDataSetter* actionData = this;
+      while (actionData) {
+        if (actionData->mSelection) {
+          actionData->mSelection = &aSelection;
+        }
+        actionData = actionData->mParentData;
+      }
+    }
+
    private:
     EditorBase& mEditorBase;
     RefPtr<Selection> mSelection;