Add support for building patched_sdk and platform.dill for dart2js:

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 c273be8460159720aecda58386bcd5956d73a098..937c4e16d79076fcd7548b3758f420878fa07500 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
@@ -270,10 +270,8 @@ class KernelTarget extends TargetImplementation {
       loader.finishStaticInvocations();
       finishAllConstructors();
       loader.finishNativeMethods();
-      transformMixinApplications();
-      // TODO(ahe): Don't call this from two different places.
-      setup_builtin_library.transformProgram(program);
-      otherTransformations();
+      runBuildTransformations();
+
       if (dumpIr) this.dumpIr();
       if (verify) this.verify();
       errors.addAll(loader.collectCompileTimeErrors().map((e) => e.format()));
@@ -389,7 +387,7 @@ class KernelTarget extends TargetImplementation {
       }
     }
     if (errors.isEmpty || dillTarget.isLoaded) {
-      setup_builtin_library.transformProgram(program);
+      runLinkTransformations(program);
     }
     ticker.logMs("Linked program");
     return program;
@@ -677,6 +675,20 @@ class KernelTarget extends TargetImplementation {
     });
   }
 
+  /// Run all transformations that are needed when building a program for the
+  /// first time.
+  void runBuildTransformations() {
+    transformMixinApplications();
+    // TODO(ahe): Don't call this from two different places.
+    setup_builtin_library.transformProgram(program);
+    otherTransformations();
+  }
+
+  /// Run all transformations that are needed when linking a program.
+  void runLinkTransformations(Program program) {
+    setup_builtin_library.transformProgram(program);
+  }
+
   void transformMixinApplications() {
     new MixinFullResolution().transform(program);
     ticker.logMs("Transformed mixin applications");