Always update 'modificationTime' in _sourceChanged().

pkg/analyzer/lib/src/context/context.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.
 
 library analyzer.src.context.context;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1807 matching lines @@
     if (entry == null) {
       return;
     }
 
     String oldContents = compareWithOld ? entry.getValue(CONTENT) : null;
 
     // Flush so that from now on we will get new contents.
     // (For example, in getLibrariesContaining.)
     entry.setState(CONTENT, CacheState.FLUSHED);
 
-    if (oldContents != null) {
-      // Fast path if the content is the same as it was last time.
-      try {
-        TimestampedData<String> fileContents = getContents(source);
-        if (fileContents.data == oldContents) {
-          int time = fileContents.modificationTime;
-          for (CacheEntry entry in _entriesFor(source)) {
-            entry.modificationTime = time;
-          }
-          return;
-        }
-      } catch (e) {
-        entry.modificationTime = -1;
+    // Prepare the new contents.
+    TimestampedData<String> fileContents;
+    try {
+      fileContents = getContents(source);
+    } catch (e) {}
+
+    // Update 'modificationTime' - we are going to update the entry.
+    {
+      int time = fileContents?.modificationTime ?? -1;
+      for (CacheEntry entry in _entriesFor(source)) {
+        entry.modificationTime = time;
       }
     }
+
+    // Fast path if the contents is the same as it was last time.
+    if (oldContents != null && fileContents?.data == oldContents) {
+      return;
+    }
+
     // We need to invalidate the cache.
     {
       if (analysisOptions.finerGrainedInvalidation &&
           AnalysisEngine.isDartFileName(source.fullName)) {
         // TODO(scheglov) Incorrect implementation in general.
         entry.setState(TOKEN_STREAM, CacheState.FLUSHED);
         entry.setState(PARSED_UNIT, CacheState.FLUSHED);
         List<Source> librarySources = getLibrariesContaining(source);
         if (librarySources.length == 1) {
           Source librarySource = librarySources[0];
@@ skipping 443 matching lines @@
     }
     DartSdk sdk = factory.dartSdk;
     if (sdk == null) {
       throw new IllegalArgumentException(
           "The source factory for an SDK analysis context must have a DartUriResolver");
     }
     return new AnalysisCache(
         <CachePartition>[AnalysisEngine.instance.partitionManager.forSdk(sdk)]);
   }
 }