Cache values of fields and lists in summary implementations.

pkg/analyzer/lib/src/summary/flat_buffers.dart

Index: pkg/analyzer/lib/src/summary/flat_buffers.dart
diff --git a/pkg/analyzer/lib/src/summary/flat_buffers.dart b/pkg/analyzer/lib/src/summary/flat_buffers.dart
index 555f1ba62b3979af0596c155a7738a341e2ed13b..9fb2950ca6aaa573f5f1494cdee75080f5b40f72 100644
--- a/pkg/analyzer/lib/src/summary/flat_buffers.dart
+++ b/pkg/analyzer/lib/src/summary/flat_buffers.dart
@@ -501,27 +501,28 @@ class StringReader extends Reader<String> {
 /**
  * An abstract reader for tables.
  */
-abstract class TableReader<T extends TableReader<T>> extends Reader<T> {
+abstract class TableReader<T> extends Reader<T> {
   const TableReader();
 
   @override
   int get size => 4;
 
   /**
-   * Return the [Reader] for reading fields of the object at [bp].
+   * Return the object at [bp].
    */
-  T createReader(BufferPointer bp);
+  T createObject(BufferPointer bp);
 
   @override
   T read(BufferPointer bp) {
     bp = bp.derefObject();
-    return createReader(bp);
+    return createObject(bp);
   }
 }
 
 class _FbList<E> extends Object with ListMixin<E> implements List<E> {
   final Reader<E> elementReader;
   final BufferPointer bp;
+  List<E> cache;
 
   _FbList(this.elementReader, this.bp);
 
@@ -534,8 +535,14 @@ class _FbList<E> extends Object with ListMixin<E> implements List<E> {
 
   @override
   E operator [](int i) {
-    BufferPointer ref = bp._advance(4 + elementReader.size * i);
-    return elementReader.read(ref);
+    cache ??= new List<E>(length);
+    E item = cache[i];
+    if (item == null) {
+      BufferPointer ref = bp._advance(4 + elementReader.size * i);
+      item = elementReader.read(ref);
+      cache[i] = item;
+    }
+    return item;
   }
 
   @override