Transform async code only for source libraries.

pkg/front_end/lib/src/fasta/kernel/kernel_target.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
index b7ec22eb16116749c8b57b6734065754180da33f..0b3215cc0bf5eda13cd987647149a53e229993ca 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
@@ -98,7 +98,7 @@ class KernelTarget extends TargetImplementation {
   final Map<String, Source> uriToSource;
 
   SourceLoader<Library> loader;
-  Program _program;
+  Program program;
 
   final List<String> errors = <String>[];
 
@@ -223,7 +223,7 @@ class KernelTarget extends TargetImplementation {
       print(message);
       errors.add(message);
     }
-    _program = erroneousProgram(isFullProgram);
+    program = erroneousProgram(isFullProgram);
   }
 
   @override
@@ -245,9 +245,9 @@ class KernelTarget extends TargetImplementation {
       installDefaultConstructors(sourceClasses);
       loader.resolveConstructors();
       loader.finishTypeVariables(objectClassBuilder);
-      _program =
+      program =
           link(new List<Library>.from(loader.libraries), nameRoot: nameRoot);
-      loader.computeHierarchy(_program);
+      loader.computeHierarchy(program);
       loader.checkOverrides(sourceClasses);
       loader.prepareInitializerInference();
       loader.performInitializerInference();
@@ -256,7 +256,7 @@ class KernelTarget extends TargetImplementation {
     } catch (e, s) {
       return reportCrash(e, s, loader?.currentUriForCrashReporting);
     }
-    return _program;
+    return program;
   }
 
   /// Build the kernel representation of the program loaded by this target. The
@@ -278,7 +278,7 @@ class KernelTarget extends TargetImplementation {
       handleInputError(null,
           isFullProgram: true, trimDependencies: trimDependencies);
       if (trimDependencies) trimDependenciesInProgram();
-      return _program;
+      return program;
     }
 
     try {
@@ -301,7 +301,7 @@ class KernelTarget extends TargetImplementation {
       return reportCrash(e, s, loader?.currentUriForCrashReporting);
     }
     if (trimDependencies) trimDependenciesInProgram();
-    return _program;
+    return program;
   }
 
   Future writeDepsFile(Uri output, Uri depsFile,
@@ -660,29 +660,29 @@ class KernelTarget extends TargetImplementation {
   }
 
   void transformMixinApplications() {
-    new MixinFullResolution(backendTarget).transform(_program);
+    new MixinFullResolution(backendTarget).transform(program);
     ticker.logMs("Transformed mixin applications");
   }
 
   void otherTransformations() {
     // TODO(ahe): Don't generate type variables in the first place.
     if (!strongMode) {
-      _program.accept(new Erasure());
+      program.accept(new Erasure());
       ticker.logMs("Erased type variables in generic methods");
     }
     // TODO(kmillikin): Make this run on a per-method basis.
-    transformAsync.transformProgram(_program);
+    transformAsync.transformProgram(program);
     ticker.logMs("Transformed async methods");
   }
 
   void verify() {
-    var verifyErrors = verifyProgram(_program);
+    var verifyErrors = verifyProgram(program);
     errors.addAll(verifyErrors.map((error) => '$error'));
     ticker.logMs("Verified program");
   }
 
   /// Tree-shakes most code from the [dillTarget] by visiting all other
-  /// libraries in [_program] and marking the APIs from the [dillTarget]
+  /// libraries in [program] and marking the APIs from the [dillTarget]
   /// libraries that are in use.
   trimDependenciesInProgram() {
     var toShake =
@@ -692,8 +692,8 @@ class KernelTarget extends TargetImplementation {
     // TODO(sigmund): replace this step with data that is directly computed from
     // the builders: we should know the tree-shaking roots without having to do
     // a second visit over the tree.
-    new RootsMarker(data).run(_program, isIncluded);
-    trimProgram(_program, data, isIncluded);
+    new RootsMarker(data).run(program, isIncluded);
+    trimProgram(program, data, isIncluded);
   }
 
   /// Return `true` if the given [library] was built by this [KernelTarget]