Use BufferContext + offset instead of BufferPointer.

pkg/analyzer/tool/summary/build_sdk_summaries.dart

Index: pkg/analyzer/tool/summary/build_sdk_summaries.dart
diff --git a/pkg/analyzer/tool/summary/build_sdk_summaries.dart b/pkg/analyzer/tool/summary/build_sdk_summaries.dart
index 9d1c34b590c46f341a2a6fee2a8787a8653d01f2..1bbd4da6967a97c46b676907b383912f620c88fa 100644
--- a/pkg/analyzer/tool/summary/build_sdk_summaries.dart
+++ b/pkg/analyzer/tool/summary/build_sdk_summaries.dart
@@ -139,9 +139,10 @@ _Output _buildMultipleOutputs(String sdkPath, bool includeSpec) {
  */
 void _extractSingleOutput(String inputPath, int field, String outputPath) {
   List<int> bytes = new File(inputPath).readAsBytesSync();
-  fb.BufferPointer root = new fb.BufferPointer.fromBytes(bytes);
-  fb.BufferPointer table = root.derefObject();
-  List<int> fieldBytes = const fb.Uint8ListReader().vTableGet(table, field);
+  fb.BufferContext root = new fb.BufferContext.fromBytes(bytes);
+  int tableOffset = root.derefObject(0);
+  List<int> fieldBytes =
+      const fb.Uint8ListReader().vTableGet(root, tableOffset, field);
   new File(outputPath).writeAsBytesSync(fieldBytes, mode: FileMode.WRITE_ONLY);
 }