Try to use incremental resolution after removing overlays.

pkg/analyzer/lib/src/generated/engine.dart

Index: pkg/analyzer/lib/src/generated/engine.dart
diff --git a/pkg/analyzer/lib/src/generated/engine.dart b/pkg/analyzer/lib/src/generated/engine.dart
index 68b16f864bba7e16157cad02f8a92c00789e7a07..e520eb507dde92315b986207ee43ad5e8109dbec 100644
--- a/pkg/analyzer/lib/src/generated/engine.dart
+++ b/pkg/analyzer/lib/src/generated/engine.dart
@@ -2170,7 +2170,7 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     }
     bool changed = newContents != originalContents;
     if (newContents != null) {
-      if (newContents != originalContents) {
+      if (changed) {
         _incrementalAnalysisCache =
             IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
         if (!analysisOptions.incremental ||
@@ -2187,7 +2187,6 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     } else if (originalContents != null) {
       _incrementalAnalysisCache =
           IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
-      changed = newContents != originalContents;
       // We are removing the overlay for the file, check if the file's
       // contents is the same as it was in the overlay.
       try {
@@ -2198,11 +2197,15 @@ class AnalysisContextImpl implements InternalAnalysisContext {
           sourceEntry.modificationTime = fileContents.modificationTime;
           changed = false;
         }
+        newContents = fileContentsData;
       } catch (e) {}
       // If not the same content (e.g. the file is being closed without save),
       // then force analysis.
       if (changed) {
-        _sourceChanged(source);
+        if (!analysisOptions.incremental ||
+            !_tryPoorMansIncrementalResolution(source, newContents)) {
+          _sourceChanged(source);
+        }
       }
     }
     if (notify && changed) {