Add operators test to source_mapping_test.

pkg/compiler/lib/src/io/position_information.dart

 // Copyright (c) 2015, 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.
 
 /// Source information system mapping that attempts a semantic mapping between
 /// offsets of JavaScript code points to offsets of Dart code points.
 
 library dart2js.source_information.position;
 
 import '../dart2jslib.dart' show
@@ skipping 154 matching lines @@
           new OffsetSourceLocation(sourceFile,
               element.resolvedAst.node.getEndToken().charOffset, name));
     }
  }
 
 
   @override
   SourceInformation buildLoop(Node node) => buildBegin(node);
 
   @override
-  SourceInformation buildGet(Node node) => buildBegin(node);
+  SourceInformation buildGet(Node node) {
+    Node left = node;
+    Node right = node;
+    Send send = node.asSend();
+    if (send != null) {
+      right = send.selector;
+    }
+    // For a read access like `a.b` the first source locations points to the
+    // left-most part of the access, `a` in the example, and the second source
+    // location points to the 'name' of accessed property, `b` in the
+    // example. The latter is needed when both `a` and `b` are compiled into
+    // JavaScript invocations.
+    return new PositionSourceInformation(
+        new OffsetSourceLocation(
+            sourceFile, left.getBeginToken().charOffset, name),
+        new OffsetSourceLocation(
+            sourceFile, right.getBeginToken().charOffset, name));
+  }
 
   @override
   SourceInformation buildCall(Node receiver, Node call) {
     return new PositionSourceInformation(
         new OffsetSourceLocation(
             sourceFile, receiver.getBeginToken().charOffset, name),
         new OffsetSourceLocation(
             sourceFile, call.getBeginToken().charOffset, name));
   }
 
@@ skipping 247 matching lines @@
 
   @override
   void onPositions(js.Node node,
                    int startPosition,
                    int endPosition,
                    int closingPosition) {
     codePositions.registerPositions(
         node, startPosition, endPosition, closingPosition);
   }
 }