getResult() should not try to compute for non-Dart files.

pkg/analyzer/lib/src/dart/analysis/driver.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:typed_data';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/error/error.dart';
@@ skipping 324 matching lines @@
   }
 
   /**
    * Notify the driver that the client is going to stop using it.
    */
   void dispose() {
     _scheduler._remove(this);
   }
 
   /**
-   * Return the [Future] that completes with a [AnalysisResult] for the file
-   * with the given [path].
+   * Return the [Future] that completes with a [AnalysisResult] for the Dart
+   * file with the given [path]. If the file is not a Dart file, the [Future]
+   * completes with `null`.
    *
    * The [path] must be absolute and normalized.
    *
    * The [path] can be any file - explicitly or implicitly analyzed, or neither.
    *
    * Causes the analysis state to transition to "analyzing" (if it is not in
    * that state already), the driver will read the file and produce the analysis
    * result for it, which is consistent with the current file state (including
    * the new state of the file), prior to the next time the analysis state
    * transitions to "idle".
    */
   Future<AnalysisResult> getResult(String path) {
-    var completer = new Completer<AnalysisResult>();
-    _requestedFiles
-        .putIfAbsent(path, () => <Completer<AnalysisResult>>[])
-        .add(completer);
-    _statusSupport.transitionToAnalyzing();
-    _scheduler._notify(this);
-    return completer.future;
+    if (AnalysisEngine.isDartFileName(path)) {
+      var completer = new Completer<AnalysisResult>();
+      _requestedFiles
+          .putIfAbsent(path, () => <Completer<AnalysisResult>>[])
+          .add(completer);
+      _statusSupport.transitionToAnalyzing();
+      _scheduler._notify(this);
+      return completer.future;
+    }
+    return new Future.value();
   }
 
   /**
    * Return the [Future] that completes with a [ParseResult] for the file
    * with the given [path].
    *
    * The [path] must be absolute and normalized.
    *
    * The [path] can be any file - explicitly or implicitly analyzed, or neither.
    *
@@ skipping 800 matching lines @@
         }
       }
 
       appendDependencies(file);
     }
   }
 
   @override
   String toString() => uri.toString();
 }