Move flat_buffer and api_signature into front_end.

pkg/analyzer/tool/summary/generate.dart

Index: pkg/analyzer/tool/summary/generate.dart
diff --git a/pkg/analyzer/tool/summary/generate.dart b/pkg/analyzer/tool/summary/generate.dart
index e6e86f3cb0c6f6f609fb6850f2f06c73d12436e7..d7c51466bea9e3ef60f53bcb5baea75f912be64f 100644
--- a/pkg/analyzer/tool/summary/generate.dart
+++ b/pkg/analyzer/tool/summary/generate.dart
@@ -433,10 +433,12 @@ class _CodeGenerator {
     outputHeader();
     out('library analyzer.src.summary.format;');
     out();
-    out("import 'flat_buffers.dart' as fb;");
-    out("import 'idl.dart' as idl;");
     out("import 'dart:convert' as convert;");
-    out("import 'api_signature.dart' as api_sig;");
+    out();
+    out("import 'package:front_end/src/base/api_signature.dart' as api_sig;");
+    out("import 'package:front_end/src/base/flat_buffers.dart' as fb;");
+    out();
+    out("import 'idl.dart' as idl;");
     out();
     for (idlModel.EnumDeclaration enm in _idl.enums.values) {
       _generateEnumReader(enm);