Fix MethodMirror.source when the method is on the first line in a script.

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 8409 matching lines @@
   intptr_t line = 1 + line_offset();
   intptr_t column = 1;
   intptr_t scan_position = 0;
   intptr_t snippet_start = -1;
   intptr_t snippet_end = -1;
   if (from_line - line_offset() == 1) {
     column += col_offset();
   }
 
   while (scan_position != length) {
+    if (snippet_start == -1) {
+      if ((line == from_line) && (column == from_column)) {
+        snippet_start = scan_position;
+      }
+    }
+
     char c = src.CharAt(scan_position);
     if (c == '\n') {
       line++;
       column = 0;
     } else if (c == '\r') {
       line++;
       column = 0;
       if ((scan_position + 1 != length) &&
           (src.CharAt(scan_position + 1) == '\n')) {
         scan_position++;
       }
     }
     scan_position++;
     column++;
 
-    if (snippet_start == -1) {
-      if ((line == from_line) && (column == from_column)) {
-        snippet_start = scan_position;
-      }
-    } else if ((line == to_line) && (column == to_column)) {
+    if ((line == to_line) && (column == to_column)) {
       snippet_end = scan_position;
       break;
     }
   }
   String& snippet = String::Handle();
   if ((snippet_start != -1) && (snippet_end != -1)) {
     snippet =
         String::SubString(src, snippet_start, snippet_end - snippet_start);
   }
   return snippet.raw();
@@ skipping 12265 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart