Reset Source modification stamp to -1 if it does not exist.

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 9b8081e988f2a6c75962234edb09bebcf4558102..2a0b7d5d609ef9f32c422948e5ccc32bd3d42ce1 100644
--- a/pkg/analyzer/lib/src/context/context.dart
+++ b/pkg/analyzer/lib/src/context/context.dart
@@ -1772,7 +1772,9 @@ class AnalysisContextImpl implements InternalAnalysisContext {
           }
           return;
         }
-      } catch (e) {}
+      } catch (e) {
+        entry.modificationTime = -1;

[Brian Wilkerson, 2015/09/23 13:53:38]

Does this need to set the modification stamp for all of the entries for the
source (similar to line 1770)? If not, is the logic on line 1770 still needed?

[scheglov, 2015/09/23 15:11:27]

In theory yes, but practically we invalidate everything at the line 1812.

I'm sorry that it hard to see now because of the work-in-progress-never-finished
limiting of invalidation.

+      }
     }
     // We need to invalidate the cache.
     {