Add AccessibleCaret::CaretElement()
Add AccessibleCaret::CaretElementInner()
Rename mCaretContentHolder -> mCaretElementHolder
Add AccessibleCaret::GetRectRelativeToRootFrame()
Add document for CaretElement() and CaretElementInner()
Assert AccessibleCaret::CreateCaretElement()
Add AccessibleCaret::LogicalPosition()

Remove unused GetFrameOffsetRect().
Add AccessibleCaret::CaretElementPosition()

We can get the position of the actual div element by calling
CaretElementPosition().
Rename mFrameOffsetRect -> mImaginaryCaretRect
Cleanse AccessibleCaret::SetPositionBasedOnFrameOffset()
Transform point coordinate in SetPosition
Rename SetPosition -> SetCaretElementPosition
Rename SetPositionBasedOnFrameOffset -> SetPosition
Assert ElementContainerFrame() in constructor
Add AccessibleCaret::RootFrame()