Invalidate the previous caret location when editing text nodes.

third_party/WebKit/Source/core/editing/FrameSelection.cpp

Index: third_party/WebKit/Source/core/editing/FrameSelection.cpp
diff --git a/third_party/WebKit/Source/core/editing/FrameSelection.cpp b/third_party/WebKit/Source/core/editing/FrameSelection.cpp
index 02fd9921d87ecfd72dc766d6b7e02429d59dab69..e19f7cfd33a16e8947b7e9b36a9aef7cb2f98ee2 100644
--- a/third_party/WebKit/Source/core/editing/FrameSelection.cpp
+++ b/third_party/WebKit/Source/core/editing/FrameSelection.cpp
@@ -731,6 +731,15 @@ void FrameSelection::invalidateCaretRect()
     m_previousCaretVisibility = m_caretBase->getCaretVisibility();
 }
 
+void FrameSelection::dataWillChange(const CharacterData& node)
+{
+    if (node == m_previousCaretNode) {
+        // This invalidation is eager, and intentionally uses stale state.
+        DisableCompositingQueryAsserts disabler;
+        m_caretBase->invalidateLocalCaretRect(m_previousCaretNode.get(), m_previousCaretRect);

[yosin_UTC9, 2016/04/29 15:03:12]

Should we reset other states of previous cares like |nodeWillBeRemoved()|?
There are:
        m_caretBase->invalidateLocalCaretRect(m_previousCaretNode.get(),
m_previousCaretRect);
        m_previousCaretNode = nullptr;
        m_previousCaretRect = LayoutRect();
        m_previousCaretVisibility = CaretVisibility::Hidden;
If so, it is better to have |resetPreviousCaretStates()| or another good name to
share code.

[chrishtr, 2016/04/29 20:09:40]

I think those other changes will still be handled correctly by
nodeWillBeRemoved. If a text
node was mutated but not deleted, there is no need to zero out the caret node as
far as I
can see.

Updating m_previousCaretRect needs to happen, but that can also be done in
invalidateCaretRect() later in the lifecycle for the current frame. 

+    }
+}
+
 void FrameSelection::paintCaret(GraphicsContext& context, const LayoutPoint& paintOffset)
 {
     if (selection().isCaret() && m_shouldPaintCaret) {