DevTools: move front-end URL handling to DevToolsUIBindingds

BUG=662859

Review-Url: https://codereview.chromium.org/2607833002
Cr-Commit-Position: refs/heads/master@{#440926}
    DocumentAvailableInMainFrame() {
  devtools_bindings_->DocumentAvailableInMainFrame();
}

    DocumentAvailableInMainFrame() {
  devtools_bindings_->DocumentAvailableInMainFrame();
}
