[Extensions] Update navigations across hypothetical extension extents

Update code to treat navigations across hypothetical extension extents
(e.g. for nonexistent extensions) the same as we do for navigations
crossing installed extension extents.

Bug: 598265

Change-Id: Ibdf2f563ce1fd108ead279077901020a24de732b
Reviewed-on: https://chromium-review.googlesource.com/617180
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#495779}
std::string WrapForJavascriptAndExtract(const char* javascript_expression) {
  return std::string("window.domAutomationController.send(") +
      javascript_expression + ")";
}

std::string WrapForJavascriptAndExtract(const char* javascript_expression) {
  return std::string("window.domAutomationController.send(") +
      javascript_expression + ")";
}
