Reland of "Move UndoStack from Page to Editor"

third_party/WebKit/Source/core/editing/commands/UndoStack.cpp

Index: third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
diff --git a/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp b/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
index 778e50f556ffbc4e5bc36735d705130aae9856a5..2be0babc7f97466b6837beff9eec08d260a8e0f1 100644
--- a/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
+++ b/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
@@ -28,7 +28,6 @@
 
 #include "core/dom/ContainerNode.h"
 #include "core/editing/commands/UndoStep.h"
-#include "platform/EventDispatchForbiddenScope.h"
 #include "wtf/TemporaryChange.h"
 
 namespace blink {
@@ -63,25 +62,6 @@ void UndoStack::registerRedoStep(UndoStep* step)
     m_redoStack.append(step);
 }
 
-void UndoStack::didUnloadFrame(const LocalFrame& frame)
-{
-    EventDispatchForbiddenScope assertNoEventDispatch;
-    filterOutUndoSteps(m_undoStack, frame);
-    filterOutUndoSteps(m_redoStack, frame);
-}
-
-void UndoStack::filterOutUndoSteps(UndoStepStack& stack, const LocalFrame& frame)
-{
-    UndoStepStack newStack;
-    while (!stack.isEmpty()) {
-        UndoStep* step = stack.first().get();
-        if (!step->belongsTo(frame))
-            newStack.append(step);
-        stack.removeFirst();
-    }
-    stack.swap(newStack);
-}
-
 bool UndoStack::canUndo() const
 {
     return !m_undoStack.isEmpty();
@@ -117,6 +97,12 @@ void UndoStack::redo()
     }
 }
 
+void UndoStack::clear()
+{
+    m_undoStack.clear();
+    m_redoStack.clear();
+}
+
 DEFINE_TRACE(UndoStack)
 {
     visitor->trace(m_undoStack);