patch_sdk.dart: Fix Windows build.

tools/patch_sdk.dart

Index: tools/patch_sdk.dart
diff --git a/tools/patch_sdk.dart b/tools/patch_sdk.dart
index 3e587840e616ba0cb1631817cb8c1ed7f238cc38..bcdc635f68c0070f280a96440520b089e461ffe2 100644
--- a/tools/patch_sdk.dart
+++ b/tools/patch_sdk.dart
@@ -241,7 +241,7 @@ Future main(List<String> argv) async {
         '--packages',
         new Uri.file(packagesFile).toString(),
         '--platform',
-        platform, // platform.dill that was just generated
+        new Uri.file(platform).toString(), // platform.dill
         Platform.script.toString() // patch_sdk.dart
       ], (CompilerContext c) async {
         CompileTask task =
@@ -253,10 +253,12 @@ Future main(List<String> argv) async {
 
       // Read depfile generated by Fasta and append deps that we have collected
       // during generation of patched_sdk to it.
-      final list = new File(depfile).readAsStringSync().split(':');
+      // Note: we are splitting by ': ' because Windows paths can start with
+      // drive letter followed by a colon.
+      final list = new File(depfile).readAsStringSync().split(': ');
       assert(list.length == 2);
       deps.addAll(list[1].split(' ').where((str) => str.isNotEmpty));
-      assert(list[0] == 'patched_sdk/platform.dill');
+      assert(list[0] == path.join('patched_sdk', 'platform.dill'));
       new File(depfile).writeAsStringSync("${list[0]}: ${deps.join(' ')}\n");
     }, zoneSpecification: new ZoneSpecification(print: (_, _2, _3, line) {
       capturedLines.add(line);