Adds WebWorker support to NetInfo v3.

Design doc: https://docs.google.com/a/chromium.org/document/d/1LTk9uVMGi4kurzcF5ellsAJReTF31fFJMHrQwSVtBjc/

BUG=368358

Review URL: https://codereview.chromium.org/299883004

git-svn-id: svn://svn.chromium.org/blink/trunk@175281 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move NoEventDispatchAssertion class to its own file

Move NoEventDispatchAssertion class to its own file instead of having it in
ContainerNode.h.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/301173006

git-svn-id: svn://svn.chromium.org/blink/trunk@175282 bbb929c8-8fbe-4397-9dbb-9b2b20218538