Trigger re-analysis when a file changes on disk.

pkg/analysis_server/lib/src/context_directory_manager.dart

Index: pkg/analysis_server/lib/src/context_directory_manager.dart
diff --git a/pkg/analysis_server/lib/src/context_directory_manager.dart b/pkg/analysis_server/lib/src/context_directory_manager.dart
index 20f51e597aed05dd5539071e08fc54a90b620e0e..7abfda8b3c479256453c9b8bc4e36e5afa996b31 100644
--- a/pkg/analysis_server/lib/src/context_directory_manager.dart
+++ b/pkg/analysis_server/lib/src/context_directory_manager.dart
@@ -134,7 +134,19 @@ abstract class ContextDirectoryManager {
         }
         break;
       case ChangeType.MODIFY:
-        // TODO(paulberry): handle modification events
+        Source source = info.sources[event.path];
+        if (source != null) {
+          ChangeSet changeSet = new ChangeSet();
+          // TODO(paulberry): technically we should skip calling changedSource()
+          // for files that currently have their contents overridden.  However,
+          // it's hard to figure out which files have their contents overridden
+          // (this info isn't exposed through the AnalysisContext interface),
+          // and besides, if we go ahead and call changedSource() we get the
+          // behavior we want (the context continues consulting the overridden
+          // file contents).
+          changeSet.changedSource(source);
+          applyChangesToContext(folder, changeSet);
+        }
         break;
     }
   }