Reduce strong mode errors and warnings

pkg/front_end/lib/src/fasta/analyzer/ast_builder.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.analyzer.ast_builder;
 
 import 'package:front_end/src/fasta/scanner/token.dart' show
     BeginGroupToken,
     Token;
 
@@ skipping 109 matching lines @@
     }
   }
 
   void handleStringJuxtaposition(int literalCount) {
     debugEvent("StringJuxtaposition");
     push(ast.adjacentStrings(popList(literalCount)));
   }
 
   void endArguments(int count, Token beginToken, Token endToken) {
     debugEvent("Arguments");
-    List expressions = popList(count);
+    List<Expression> expressions = popList(count);
     ArgumentList arguments = ast.argumentList(toAnalyzerToken(beginToken),
         expressions, toAnalyzerToken(endToken));
     push(ast.methodInvocation(null, null, null, null, arguments));
   }
 
   void beginExpression(Token token) {
     isFirstIdentifier = true;
   }
 
   void handleIdentifier(Token token) {
@@ skipping 39 matching lines @@
   void doPropertyGet(Token token) {
   }
 
   void endExpressionStatement(Token token) {
     debugEvent("ExpressionStatement");
     push(ast.expressionStatement(pop(), toAnalyzerToken(token)));
   }
 
   void endFunctionBody(int count, Token beginToken, Token endToken) {
     debugEvent("FunctionBody");
-    List statements = popList(count);
+    List<Statement> statements = popList(count);
     if (beginToken != null) {
       exitLocalScope();
     }
     push(ast.block(toAnalyzerToken(beginToken), statements,
             toAnalyzerToken(endToken)));
   }
 
   void finishFunction(formals, asyncModifier, Statement body) {
     debugEvent("finishFunction");
     var kernel = toKernel(body, elementStore, library.library, scope);
@@ skipping 385 matching lines @@
     debugEvent("Modifier");
     // TODO(ahe): Don't ignore modifiers.
   }
 
   void handleModifiers(int count) {
     debugEvent("Modifiers");
     // TODO(ahe): Don't ignore modifiers.
     push(NullValue.Modifiers);
   }
 }