Revert "Fix creating InjectedScript too early causing extension bindings not to work."

This reverts commit 5bee3a037490e86ca3ab26252cc510986979f4dd.

Reverting to fix failing telemetry_unittests on mac_rel so that
Blink rolls can go through.

BUG=
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/23202002

git-svn-id: svn://svn.chromium.org/blink/trunk@156105 bbb929c8-8fbe-4397-9dbb-9b2b20218538