Fix strong-mode bug in dart2js ConstantMap.from.

Fixes 33371.

Bug: http://dartbug.com/33371
Change-Id: I57eeeb2a0eca198c76c3470706648110da45775b
Reviewed-on: https://dart-review.googlesource.com/59082
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>

sdk/lib/_internal/js_runtime/lib/constant_map.dart

@@ -12,7 +12,7 @@ class ConstantMapView<K, V> extends UnmodifiableMapView<K, V>
 abstract class ConstantMap<K, V> implements Map<K, V> {
   // Used to create unmodifiable maps from other maps.
   factory ConstantMap.from(Map other) {
-    List keys = other.keys.toList();
+    List keys = new List<K>.from(other.keys);
     bool allStrings = true;
     for (var k in keys) {
       if (k is! String) {
@@ -26,7 +26,7 @@ abstract class ConstantMap<K, V> implements Map<K, V> {
       var object = JS('=Object', '{}');
       int length = 0;
       for (var k in keys) {
-        var v = other[k];
+        V v = other[k];
         if (k != '__proto__') {
           if (!jsHasOwnProperty(object, k)) length++;
           JS('void', '#[#] = #', object, k, v);

tests/corelib_2/corelib_2.status

@@ -224,8 +224,6 @@ nan_infinity_test/01: RuntimeError
 string_split_test/checkedstore: RuntimeError
 symbol_reserved_word_test/03: RuntimeError # Issue 19972, new Symbol('void') should be allowed.
 uri_base_test: Crash # RangeError (index): Invalid value: Valid value range is empty: 0
-uri_parameters_all_test: RuntimeError
-uri_test: RuntimeError
 
 [ $compiler == dart2js && $fasta ]
 int_from_environment_int64_test: RuntimeError # WontFix: Int not precisely representable in JS
@@ -254,8 +252,6 @@ regexp/pcre_test: RuntimeError
 string_split_test/checkedstore: RuntimeError # Issue 30548: does not check stores into List<String>
 symbol_reserved_word_test/03: RuntimeError # Issue 19972, new Symbol('void') should be allowed.
 uri_base_test: RuntimeError
-uri_parameters_all_test: RuntimeError
-uri_test: RuntimeError
 
 [ $compiler == dart2js && $fasta && $minified && $strong ]
 cast_test: RuntimeError
@@ -280,8 +276,6 @@ symbol_operator_test/03: RuntimeError
 symbol_operator_test/none: RuntimeError
 symbol_reserved_word_test/03: RuntimeError # Issue 19972, new Symbol('void') should be allowed.
 uri_base_test: RuntimeError
-uri_parameters_all_test: RuntimeError
-uri_test: RuntimeError
 
 [ $compiler == dart2js && $fasta && !$strong ]
 *: SkipByDesign