Mark editing/selection/fake-doubleclick.html as flaky

BUG=252038
TBR=

Review URL: https://codereview.chromium.org/17449016

git-svn-id: svn://svn.chromium.org/blink/trunk@152737 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make CustomElementHelpers divest constructor generation code.

CustomElementHelpers is an unstructured mess. Make sense of it by
breaking it into pieces for constructor generation, wrapper creation,
callbacks, etc.

This pulls the methods related to constructor generation into their
own class. This does not bring sanity to the code that moved nor the
code that remains; just transferring the inmates to the right asylum
first without changing behavior.

BUG=234509
R=dglazkov@chromium.org, haraken@chromium.org

Review URL: https://codereview.chromium.org/16938010

git-svn-id: svn://svn.chromium.org/blink/trunk@152738 bbb929c8-8fbe-4397-9dbb-9b2b20218538