Reapply CL: first step for modular support in fasta

pkg/front_end/test/fasta/testing/suite.dart

Index: pkg/front_end/test/fasta/testing/suite.dart
diff --git a/pkg/front_end/test/fasta/testing/suite.dart b/pkg/front_end/test/fasta/testing/suite.dart
index 50f369bd2f1556a38b35d7df36d5c79ecbaa5a1a..d9a1c09c2d05871bfa9e0420f213f1815fe9c748 100644
--- a/pkg/front_end/test/fasta/testing/suite.dart
+++ b/pkg/front_end/test/fasta/testing/suite.dart
@@ -44,7 +44,7 @@ import 'package:front_end/src/fasta/kernel/kernel_target.dart'
 
 import 'package:front_end/src/fasta/dill/dill_target.dart' show DillTarget;
 
-import 'package:kernel/kernel.dart' show loadProgramFromBinary;
+import 'package:kernel/kernel.dart' show loadProgramFromBytes;
 
 export 'package:testing/testing.dart' show Chain, runMe;
 
@@ -85,12 +85,11 @@ class FastaContext extends ChainContext {
   Uri sdk;
   Uri platformUri;
   Uri outlineUri;
+  List<int> outlineBytes;
 
   final ExpectationSet expectationSet =
       new ExpectationSet.fromJsonList(JSON.decode(EXPECTATIONS));
 
-  Future<Program> outline;
-
   FastaContext(
       this.vm,
       bool strongMode,
@@ -125,11 +124,16 @@ class FastaContext extends ChainContext {
     }
   }
 
-  Future<Program> loadPlatformOutline() {
-    return outline ??= new Future<Program>(() async {
+  Future<Program> loadPlatformOutline() async {
+    if (outlineBytes == null) {
       await ensurePlatformUris();
-      return loadProgramFromBinary(outlineUri.toFilePath());
-    });
+      outlineBytes = new File.fromUri(outlineUri).readAsBytesSync();
+    }
+    // Note: we rebuild the platform outline on every test because the compiler
+    // currently mutates the in-memory representation of the program without
+    // cloning it.
+    // TODO(sigmund): investigate alternatives to this approach.
+    return loadProgramFromBytes(outlineBytes);
   }
 
   static Future<FastaContext> create(
@@ -225,7 +229,7 @@ class Outline extends Step<TestDescription, Program, FastaContext> {
       }
       p = await sourceTarget.buildOutlines();
       if (fullCompile) {
-        p = await sourceTarget.buildProgram();
+        p = await sourceTarget.buildProgram(trimDependencies: true);
         instrumentation?.finish();
         if (instrumentation != null && instrumentation.hasProblems) {
           if (updateComments) {