Some member functions of TreeScopeEventContext are defined in the diffrent header file.

These member functions should be defined in TreeScopeEventContext.h.

Review URL: https://codereview.chromium.org/144843002

git-svn-id: svn://svn.chromium.org/blink/trunk@165520 bbb929c8-8fbe-4397-9dbb-9b2b20218538