compositionstart event's data should contain text to replace.

Source/core/editing/Editor.cpp

Index: Source/core/editing/Editor.cpp
diff --git a/Source/core/editing/Editor.cpp b/Source/core/editing/Editor.cpp
index 7baf56420357f5d5d84106362208503a1d2470b8..f1678fe550eb71964fff83f03081a60a05ada366 100644
--- a/Source/core/editing/Editor.cpp
+++ b/Source/core/editing/Editor.cpp
@@ -1247,7 +1247,13 @@ void Editor::setComposition(const String& text, const Vector<CompositionUnderlin
             // We should send a compositionstart event only when the given text is not empty because this
             // function doesn't create a composition node when the text is empty.
             if (!text.isEmpty()) {
-                target->dispatchEvent(CompositionEvent::create(eventNames().compositionstartEvent, m_frame->document()->domWindow(), text));
+                FrameSelection* selection = m_frame->selection();
+                String selectionText;
+                if (selection->isRange()) {
+                    RefPtr<Range> range = selection->toNormalizedRange();
+                    selectionText = plainText(range.get());
+                }
+                target->dispatchEvent(CompositionEvent::create(eventNames().compositionstartEvent, m_frame->document()->domWindow(), selectionText));

[rniwa-cr, 2013/07/15 21:46:52]

You could have simply called selectedText() here as I've done so in
https://bugs.webkit.org/show_bug.cgi?id=118684.

[kochi, 2013/07/16 09:50:41]

Done.

                 event = CompositionEvent::create(eventNames().compositionupdateEvent, m_frame->document()->domWindow(), text);
             }
         } else {