Apply tweaks to address other review comments.

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:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 108 matching lines @@
    * The set of explicitly analyzed files.
    */
   final _explicitFiles = new LinkedHashSet<String>();
 
   /**
    * The set of files that are currently scheduled for analysis.
    */
   final _filesToAnalyze = new LinkedHashSet<String>();
 
   /**
-   * The mapping of [Uri]s to the mapping of textual URIs to the [Source]
-   * that correspond in the current [_sourceFactory].
+   * Cache of URI resolution. The outer map key is the absolute URI of the
+   * containing file. The inner map key is the URI text of a directive
+   * contained in that file. The inner map value is the [Source] object which
+   * that URI text resolves to.
    */
   final _uriResolutionCache = <Uri, Map<String, Source>>{};
 
   /**
    * The current file state.
    *
    * It maps file paths to the MD5 hash of the file content.
    */
   final _fileContentHashMap = <String, String>{};
 
@@ skipping 193 matching lines @@
 
       AnalysisContext analysisContext = _createAnalysisContext(libraryContext);
       analysisContext.setContents(file.source, file.content);
       try {
         // Compute resolved unit.
 //        _logger.runTimed('Computed resolved unit', () {
 //          analysisContext.resolveCompilationUnit2(
 //              libraryContext.file.source, libraryContext.file.source);
 //        });
         // Compute errors.
-        List<AnalysisError> errors;
-        try {
-          errors = _logger.run('Compute errors', () {
-            return analysisContext.computeErrors(file.source);
-          });
-        } catch (e, st) {
-          // TODO(scheglov) why does it fail?
-          // Caused by Bad state: Unmatched TypeParameterElementImpl T
-          errors = [];
-        }
+        List<AnalysisError> errors = _logger.run('Compute errors', () {
+          return analysisContext.computeErrors(file.source);
+        });
         List<String> errorStrings = errors
             .where((error) => error.errorCode is! TodoCode)
             .map((error) => error.toString())
             .toList();
         {
           fb.Builder fbBuilder = new fb.Builder();
           var exportedOffset = fbBuilder.writeList(errorStrings
               .map((errorStr) => fbBuilder.writeString(errorStr))
               .toList());
           fbBuilder.startTable();
@@ skipping 430 matching lines @@
 
     return _unit;
   }
 
   Uri get uri => source.uri;
 
   /**
    * Return the [_File] for the [uri] referenced in this file.
    */
   _File resolveUri(String uri) {
+    // TODO(scheglov) Consider removing this caching after implementing other
+    // optimizations, e.g. changeFile() optimization.
     Source uriSource = driver._uriResolutionCache
         .putIfAbsent(this.uri, () => <String, Source>{})
         .putIfAbsent(uri, () => driver._sourceFactory.resolveUri(source, uri));
     return new _File(driver, uriSource);
   }
 
   @override
   String toString() => uri.toString();
 
   /**
@@ skipping 141 matching lines @@
 
 /**
  * TODO(scheglov) document
  */
 class _ReferencedUris {
   bool isLibrary = true;
   final List<String> imported = <String>[];
   final List<String> exported = <String>[];
   final List<String> parted = <String>[];
 }