Fix strong-mode warnings.

lib/parser.dart

Index: lib/parser.dart
diff --git a/lib/parser.dart b/lib/parser.dart
index a9fcff57840ec6d4cef109b24770db20c16a9440..c69420c6e2142d3849ca66624b3587c9db79188e 100644
--- a/lib/parser.dart
+++ b/lib/parser.dart
@@ -182,7 +182,7 @@ class SingleMapping extends Mapping {
     var names = new LinkedHashMap<String, int>();
 
     var lineNum;
-    var targetEntries;
+    List<TargetEntry> targetEntries;
     for (var sourceEntry in sourceEntries) {
       if (lineNum == null || sourceEntry.target.line > lineNum) {
         lineNum = sourceEntry.target.line;
@@ -212,8 +212,8 @@ class SingleMapping extends Mapping {
 
   SingleMapping.fromJson(Map map, {mapUrl})
       : targetUrl = map['file'],
-        urls = map['sources'],
-        names = map['names'],
+        urls = map['sources'] as List<String>,

[Siggi Cherem (dart-lang), 2016/03/24 01:15:02]

+leafp - would this cause a runtime check failure?

Json decoders allocate generic lists and maps with dynamic type arguments (since
we don't know what the List contains until you parse the contents).

[Leaf, 2016/03/24 03:23:41]

Yep.  If map['sources'] returns something with reified type List<dynamic>, this
cast will fail in ddc.  If copying the list doesn't matter (that is, you're not
relying on mutations to the original list showing up in your new list), then you
can do a new List<String>.from(...) here.  Otherwise... it gets a bit tricky. 
I'm starting to wonder whether we should write delegating wrappers for common
types like this that do type checks on reads.  That doesn't handle any identity
issues, but it at least allows sharing the underlying mutable state.

[nweiz, 2016/03/24 19:07:54]

Good catch, done.

@leafp: That would also be nice for just avoiding the overhead of copying. I've
filed https://github.com/dart-lang/collection/issues/25 to track it.

[Siggi Cherem (dart-lang), 2016/03/24 19:36:19]

+1 - it would be good to avoid coping.

+        names = map['names'] as List<String>,
         sourceRoot = map['sourceRoot'],
         lines = <TargetLineEntry>[],
         _mapUrl = mapUrl is String ? Uri.parse(mapUrl) : mapUrl {