Resynthesize most of the ImportElementImpl lazily.

pkg/analyzer/test/src/summary/resynthesize_test.dart

Index: pkg/analyzer/test/src/summary/resynthesize_test.dart
diff --git a/pkg/analyzer/test/src/summary/resynthesize_test.dart b/pkg/analyzer/test/src/summary/resynthesize_test.dart
index 4990c5b906fd9bd2c2ff9e84c8b9191e44838ec6..ad450a45d39bddc88fc03d96606944c9e7e25bcd 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_test.dart
@@ -1082,9 +1082,10 @@ abstract class AbstractResynthesizeTest extends AbstractSingleUnitTest {
   void compareUriReferencedElements(UriReferencedElementImpl resynthesized,
       UriReferencedElementImpl original, String desc) {
     compareElements(resynthesized, original, desc);
-    expect(resynthesized.uri, original.uri);
-    expect(resynthesized.uriOffset, original.uriOffset, reason: desc);
-    expect(resynthesized.uriEnd, original.uriEnd, reason: desc);
+    expect(resynthesized.uri, original.uri, reason: '$desc uri');
+    expect(resynthesized.uriOffset, original.uriOffset,
+        reason: '$desc uri uriOffset');
+    expect(resynthesized.uriEnd, original.uriEnd, reason: '$desc uriEnd');
   }
 
   void compareVariableElements(