Make Script::GetTokenLocation() and Script::TokenRangeAtLine() use token streams where possible.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index d5c8caddd1e01de4eabb53595fba39ee22f717d8..157612101ee09ca89867c325f147f2e7a43735c3 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2261,6 +2261,10 @@ class Script : public Object {
   void GetTokenLocation(intptr_t token_pos,
                         intptr_t* line, intptr_t* column) const;
 
+  // Returns index of first and last token on the given line. Returns both
+  // indices < 0 if no token exists on or after the line. If a token exists
+  // after, but not on given line, returns in *first_token_index the index of
+  // the first token after the line, and a negative value in *last_token_index.
   void TokenRangeAtLine(intptr_t line_number,
                         intptr_t* first_token_index,
                         intptr_t* last_token_index) const;