[omnibox] Break out SetCaretPos() method and enhance browser test

components/omnibox/browser/omnibox_view.h

Index: components/omnibox/browser/omnibox_view.h
diff --git a/components/omnibox/browser/omnibox_view.h b/components/omnibox/browser/omnibox_view.h
index c764782ec848d5832725252bd5aafe27193b13b4..7a0a1dbc5f6bd42d0eaed3a266d5786038d3a8af 100644
--- a/components/omnibox/browser/omnibox_view.h
+++ b/components/omnibox/browser/omnibox_view.h
@@ -104,6 +104,10 @@ class OmniboxView {
                                         bool update_popup,
                                         bool notify_text_changed) = 0;
 
+  // Sets the caret position. Removes any selection. Will not put caret
+  // past the current text.

[Peter Kasting, 2017/05/18 18:38:34]

Nit: This last sentence isn't perfectly clear about whether requests to do this
will be clamped or no-oped, so I'd instead say "Clamps the requested caret
position to the length of the current text."

[Kevin Bailey, 2017/05/18 19:48:17]

Done. ("Removes..." probably isn't necessary. Let me know if it clutters the
comment.)

+  virtual void SetCaretPos(size_t caret_pos) = 0;
+
   // Transitions the user into keyword mode with their default search provider,
   // preserving and selecting the user's text if they already typed in a query.
   virtual void EnterKeywordModeForDefaultSearchProvider() = 0;