Adds InstantExtendedEnabledParam to the search request URL iff the query extraction flag is enabled.

chrome/browser/search/search.h

Index: chrome/browser/search/search.h
diff --git a/chrome/browser/search/search.h b/chrome/browser/search/search.h
index 0e9e8260b2b702197c306eebff6a19560acbc7ae..6608bebcc9eaa4123f0d25d9da9bd986f57f4d3d 100644
--- a/chrome/browser/search/search.h
+++ b/chrome/browser/search/search.h
@@ -71,6 +71,15 @@ bool IsSuggestPrefEnabled(Profile* profile);
 // the Instant Extended API is not enabled.
 uint64 EmbeddedSearchPageVersion();
 
+// Returns a string indicating whether InstantExtended is enabled, suitable
+// for adding as a query string param to the homepage or search requests.
+//
+// On desktop, |for_search| is set to true for search requests and this
+// function returns an empty string when the query extraction is disabled.
+// On mobile, |for_search| param is unused because the query extraction is
+// always enabled.
+std::string InstantExtendedEnabledParam(bool for_search);
+
 // Returns whether query extraction is enabled.
 bool IsQueryExtractionEnabled();