Tweak public APIs and use them in patch_sdk, dart2js, and kernel-service

pkg/front_end/lib/summary_generator.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// Defines the front-end API for converting source code to summaries.
 library front_end.summary_generator;
 
 import 'dart:async';
 import 'compiler_options.dart';
 
+import 'src/kernel_generator_impl.dart';
+
 /// Creates a summary representation of the build unit whose source files are in
 /// [sources].
 ///
 /// Intended to be a part of a modular compilation process.
 ///
 /// [sources] should be the complete set of source files for a build unit
 /// (including both library and part files).
 ///
-/// The summarization process is hermetic, meaning that the only files which
-/// will be read are those listed in [sources],
+/// By default, the compilation process is hermetic, meaning that the only files
+/// which will be read are those listed in [sources],
 /// [CompilerOptions.inputSummaries], and [CompilerOptions.sdkSummary].  If a
 /// source file attempts to refer to a file which is not obtainable from these
-/// paths, that will result in an error, even if the file exists on the
+/// URIs, that will result in an error, even if the file exists on the
 /// filesystem.
 ///
+/// When [CompilerOptions.chaseDependencies] is true, this default behavior
+/// changes, and any dependency of [sources] that is not listed in
+/// [CompilerOptions.inputSummaries] and [CompilerOptions.sdkSummary] is treated
+/// as an additional source file for the build unit.
+///
 /// Any `part` declarations found in [sources] must refer to part files which
-/// are also listed in [sources], otherwise an error results.  (It is not
-/// permitted to refer to a part file declared in another build unit).
+/// are also listed in the build unit sources, otherwise an error results.  (It
+/// is not permitted to refer to a part file declared in another build unit).
 ///
 /// The return value is a list of bytes to write to the summary file.

[ahe, 2017/07/03 10:05:31]

If we're concerned about memory usage, this API should take a Sink or an
EventSink instead of returning a List.

[Siggi Cherem (dart-lang), 2017/07/05 03:39:30]

True - we also have some open discussion about whether we want the file-system
API or an input-provider/output-provider API instead.

Like with the other suggestions, I'd like to keep this separate from this CL.

-Future<List<int>> summaryFor(List<Uri> sources, CompilerOptions options) =>
-    throw new UnimplementedError();
+Future<List<int>> summaryFor(List<Uri> sources, CompilerOptions options) async {
+  return (await generateKernel(sources, options,
+          buildSummary: true, buildProgram: false))
+      ?.summary;
+}