Enable strong-mode for pkg/kernel and fix some strong-mode warnings.

BUG=
R=kmillikin@google.com

Review URL: https://codereview.chromium.org/2523673005 .

pkg/kernel/.analysis_options

@@ -1,4 +1,5 @@
 analyzer:
+  strong-mode: true
   language:
     enableSuperMixins: true
   exclude:

pkg/kernel/bin/dartk.dart

@@ -262,7 +262,8 @@ Future<CompilerOutcome> batchMain(
   String format = options['format'] ?? defaultFormat();
   String outputFile = options['out'] ?? defaultOutput();
 
-  var customUriMappings = parseCustomUriMappings(options['url-mapping']);
+  List<String> urlMapping = options['url-mapping'] as List<String>;
+  var customUriMappings = parseCustomUriMappings(urlMapping);
   var repository = new Repository();
 
   Program program;

pkg/kernel/lib/transformations/continuation.dart

@@ -153,7 +153,7 @@ class SyncStarFunctionRewriter extends ContinuationRewriterBase {
   visitYieldStatement(YieldStatement node) {
     var transformedExpression = node.expression.accept(this);
 
-    var statements = [];
+    var statements = <Statement>[];
     if (node.isYieldStar) {
       var markYieldEach = new ExpressionStatement(new PropertySet(
           new VariableGet(iteratorVariable),
@@ -498,9 +498,8 @@ abstract class AsyncRewriterBase extends ContinuationRewriterBase {
     }
     loopBody.add(
         new IfStatement(cond, new Block(newBody), new BreakStatement(labeled)));
-    labeled.body =
-        new WhileStatement(new BoolLiteral(true), new Block(loopBody))
-        ..parent = labeled;
+    labeled.body = new WhileStatement(
+        new BoolLiteral(true), new Block(loopBody))..parent = labeled;
     statements.add(new Block(<Statement>[]
       ..addAll(temps)
       ..add(labeled)));
@@ -831,24 +830,28 @@ class HelperNodes {
       }
       throw 'Library "$name" not found';
     }
+
     Class findClass(Library library, String name) {
       for (var klass in library.classes) {
         if (klass.name == name) return klass;
       }
       throw 'Class "$name" not found';
     }
+
     Procedure findFactoryConstructor(Class klass, String name) {
       for (var procedure in klass.procedures) {
         if (procedure.isStatic && procedure.name.name == name) return procedure;
       }
       throw 'Factory constructor "$klass.$name" not found';
     }
+
     Constructor findConstructor(Class klass, String name) {
       for (var constructor in klass.constructors) {
         if (constructor.name.name == name) return constructor;
       }
       throw 'Constructor "$klass.$name" not found';
     }
+
     Procedure findProcedure(Library library, String name) {
       for (var procedure in library.procedures) {
         if (procedure.name.name == name ||

pkg/kernel/test/batch_consistency.dart

@@ -35,10 +35,8 @@ main(List<String> args) async {
 }
 
 Future<bool> areFilesEqual(String first, String second) async {
-  List<List<int>> bytes = await Future.wait([
-    new File(first).readAsBytes(),
-    new File(second).readAsBytes()
-  ]);
+  List<List<int>> bytes = await Future
+      .wait([new File(first).readAsBytes(), new File(second).readAsBytes()]);
   if (bytes[0].length != bytes[1].length) return false;
   for (int i = 0; i < bytes[0].length; ++i) {
     if (bytes[0][i] != bytes[1][i]) return false;
@@ -58,7 +56,9 @@ testBatchModeConsistency(List<String> options, List<String> files) {
       List results = [null, null];
       bool failed = false;
       for (int i = 0; i < 2; ++i) {
-        var args = []..addAll(options)..addAll(['--out', outputFiles[i], file]);
+        var args = <String>[]
+          ..addAll(options)
+          ..addAll(['--out', outputFiles[i], file]);
         var state = (i == 0) ? sharedState : new dartk.BatchModeState();
         try {
           // We run the two executions in a loop to ensure any stack traces

pkg/kernel/test/type_parser.dart

@@ -174,8 +174,7 @@ class DartTypeParser {
     }
   }
 
-  void parseParameterList(
-      List<DartType> positional, List<NamedType> named) {
+  void parseParameterList(List<DartType> positional, List<NamedType> named) {
     int token = scanToken();
     assert(token == Token.LeftParen);
     token = peekToken();
@@ -215,7 +214,7 @@ class DartTypeParser {
       types.add(parseType());
       token = scanToken();
       if (token != Token.Comma && token != close) {
-        return fail('Unterminated list');
+        throw fail('Unterminated list');
       }
     }
     return types;
@@ -243,7 +242,7 @@ class DartTypeParser {
       typeParameters.add(parseAndPushTypeParameter());
       token = scanToken();
       if (token != Token.Comma && token != Token.RightAngle) {
-        return fail('Unterminated type parameter list');
+        throw fail('Unterminated type parameter list');
       }
     }
     return typeParameters;
@@ -275,8 +274,8 @@ class DartTypeParser {
 class LazyTypeEnvironment {
   final Map<String, Class> classes = <String, Class>{};
   final Map<String, TypeParameter> typeParameters = <String, TypeParameter>{};
-  final Library dummyLibrary = new Library(new Uri(path: 'dummy.dart'),
-    name: 'lib');
+  final Library dummyLibrary =
+      new Library(new Uri(path: 'dummy.dart'), name: 'lib');
 
   TreeNode lookup(String name) {
     return name.length == 1