Move flat_buffer and api_signature into front_end.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index 92ae832e90ccc91aa3f4fa54dc9bd8f4c10731e2..469822ed1ad55bf6f2e2c5d3c6c1b7c1e3844e1e 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -27,10 +27,10 @@ import 'package:analyzer/src/generated/engine.dart'
     show AnalysisContext, AnalysisEngine, AnalysisOptions;
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/lint/registry.dart' as linter;
-import 'package:analyzer/src/summary/api_signature.dart';
 import 'package:analyzer/src/summary/format.dart';
 import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/package_bundle_reader.dart';
+import 'package:front_end/src/base/api_signature.dart';
 import 'package:front_end/src/incremental/byte_store.dart';
 import 'package:meta/meta.dart';