Better breakpoint placement

runtime/vm/scanner.h

Index: runtime/vm/scanner.h
===================================================================
--- runtime/vm/scanner.h	(revision 9175)
+++ runtime/vm/scanner.h	(working copy)
@@ -64,9 +64,14 @@
   // Use CurrentPosition() to extract position.
   void ScanTo(intptr_t token_index);
 
-  // Returns token index of first token on or after given line number.
-  // Returns negative value if no token exists on or after the line.
-  intptr_t TokenIndexAtLine(intptr_t line_number);
+  // 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
+  // *fisrt_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);
 
   // Scans entire source and returns a stream of tokens.
   // Should be called only once.