Create AccessibleCaret after canvas frame exists
Add Glue so we can write gtest easily.
Consider no inflation when performing hit test
Update copyright header

Reference:
https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Coding_Style#Mode_Line
Add GetSelectionIsCollapsed and GetSelectionRangeCount().
Reorg UpdateCarets.
Add gtest framework.
Flip condition on MOZ_ASSERT.
Explicitly check all resources required in constructor

Also assign mAnonymousContent explicitly in the constructor.
Give mAnonymousContent a meaningful name as mCaretContentHolder
Delete unneeded null check against mCaretContentHolder

We've assert it in InjectCaretElement.
No need to reset mPresShell
Improve AccessibleCaret::SetPosition()