Validate modifications times only for sources.

pkg/analyzer/lib/src/context/context.dart

Index: pkg/analyzer/lib/src/context/context.dart
diff --git a/pkg/analyzer/lib/src/context/context.dart b/pkg/analyzer/lib/src/context/context.dart
index b320e9b30aec1fcf668bc272f21b783959ecae08..82e486a59ae03c71a8e91efc3b517fe7410ac50f 100644
--- a/pkg/analyzer/lib/src/context/context.dart
+++ b/pkg/analyzer/lib/src/context/context.dart
@@ -1824,8 +1824,9 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     HashSet<Source> missingSources = new HashSet<Source>();
     MapIterator<AnalysisTarget, CacheEntry> iterator = _cache.iterator();
     while (iterator.moveNext()) {
-      Source source = iterator.key.source;
-      if (source != null) {
+      AnalysisTarget target = iterator.key;
+      if (target is Source) {
+        Source source = target;

[Brian Wilkerson, 2015/05/12 01:03:22]

Or just use 'target' in the then block...

         CacheEntry entry = iterator.value;
         int sourceTime = getModificationStamp(source);
         if (sourceTime != entry.modificationTime) {