Make patch_sdk step invoke fasta's compile_platform to generate patched_sdk/platform.dill.

pkg/front_end/lib/src/fasta/compile_platform.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.
 
 library fasta.compile_platform;
 
 import 'dart:async' show
     Future;
 
 import 'package:kernel/verifier.dart' show
@@ skipping 45 matching lines @@
 Future compilePlatform(CompilerContext c, Ticker ticker) async {
   ticker.isVerbose = c.options.verbose;
   Uri output = Uri.base.resolveUri(new Uri.file(c.options.arguments[1]));
   Uri patchedSdk =
       Uri.base.resolveUri(new Uri.file(c.options.arguments[0]));
   ticker.logMs("Parsed arguments");
   if (ticker.isVerbose) {
     print("Compiling $patchedSdk to $output");
   }
 
-  TranslateUri uriTranslator = await TranslateUri.parse(patchedSdk);
+  TranslateUri uriTranslator = await TranslateUri.parse(
+      patchedSdk, c.options.packages);
   ticker.logMs("Read packages file");
 
   DillTarget dillTarget = new DillTarget(ticker, uriTranslator);
   KernelTarget kernelTarget = new KernelTarget(
       dillTarget, uriTranslator, c.uriToSource);
 
   kernelTarget.read(Uri.parse("dart:core"));
   await dillTarget.writeOutline(null);
   await kernelTarget.writeOutline(output);
 
   if (exitCode != 0) return null;
   await kernelTarget.writeProgram(output, AstKind.Kernel);
   if (c.options.dumpIr) {
     kernelTarget.dumpIr();
   }
   if (c.options.verify) {
     try {
       verifyProgram(kernelTarget.program);
       ticker.logMs("Verified program");
     } catch (e, s) {
       exitCode = 1;
       print("Verification of program failed: $e");
       if (s != null && c.options.verbose) {
         print(s);
       }
     }
   }
 }