GitLab

This CL,
- Adds a new EmbeddedSearchPageVerion variant to enable EmbeddedSearch API in Android Chrome search results page.
- Adds an experiment flag to enable "EmbeddedSearch API" for Android Chrome.
- Creates SearchTabHelper for TabAndroid WebContents.
- Uses EmbeddedSearch API to submit search queries if the underlying search results page supports Instant.
- Assigns Instant search URL renderers to a priviledged Instant process.
- Uses "chrome-search://" scheme for Instant search URLs.
- Creates new test to verify the embedded search page version.

To test: Enable EmbeddedSearch API flag from about://flags page and run Android Chrome against demo server URL (cl/64511863).
Server side bug: b/10402468

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/215733002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@267069 0039d316-1c4b-4281-b951-d872f2087c98