Cache snapshots of (mostly) immutable transformer phases.

sdk/lib/_internal/pub_generated/lib/src/dart.dart

Index: sdk/lib/_internal/pub_generated/lib/src/dart.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/dart.dart b/sdk/lib/_internal/pub_generated/lib/src/dart.dart
index f5cf58255e18eb085ae048ed504d355f6ac17dcf..38eaf07f48bac3004743cc14ecdddd085313c7c9 100644
--- a/sdk/lib/_internal/pub_generated/lib/src/dart.dart
+++ b/sdk/lib/_internal/pub_generated/lib/src/dart.dart
@@ -1,5 +1,6 @@
 library pub.dart;
 import 'dart:async';
+import 'dart:io';
 import 'dart:isolate';
 import 'package:analyzer/analyzer.dart';
 import 'package:path/path.dart' as path;
@@ -8,6 +9,7 @@ import '../../../compiler/compiler.dart' as compiler;
 import '../../../compiler/implementation/filenames.dart' show appendSlash;
 import '../../asset/dart/serialize.dart';
 import 'io.dart';
+import 'log.dart' as log;
 import 'utils.dart';
 abstract class CompilerProvider {
   Uri get libraryRoot;
@@ -72,7 +74,11 @@ class _DirectiveCollector extends GeneralizingAstVisitor {
   final directives = <UriBasedDirective>[];
   visitUriBasedDirective(UriBasedDirective node) => directives.add(node);
 }
-Future runInIsolate(String code, message) {
+Future runInIsolate(String code, message, {String snapshot}) {
+  if (snapshot != null && fileExists(snapshot)) {
+    log.fine("Spawning isolate from $snapshot.");
+    return Chain.track(Isolate.spawnUri(path.toUri(snapshot), [], message));
+  }
   return withTempDir((dir) {
     var dartPath = path.join(dir, 'runInIsolate.dart');
     writeTextFile(dartPath, code, dontLogContents: true);
@@ -87,6 +93,17 @@ Future runInIsolate(String code, message) {
       return new Future.error(
           new CrossIsolateException.deserialize(response['error']),
           new Chain.current());
+    }).then((_) {
+      if (snapshot == null) return null;
+      ensureDir(path.dirname(snapshot));
+      return runProcess(
+          Platform.executable,
+          ['--snapshot=$snapshot', dartPath]).then((result) {
+        if (result.success) return;
+        log.warning(
+            "Failed to compile a snapshot to " "${path.relative(snapshot)}:\n" +
+                result.stderr.join("\n"));
+      });
     });
   });
 }