Reduce strong mode errors and warnings

pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart

Index: pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
index 24c48bab89243726e437c1290353d7be11349c1e..fb10a73936ec5ab19bd8749b6319467af76030d0 100644
--- a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
+++ b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
@@ -127,7 +127,7 @@ class AstBuilder extends ScopeListener {
 
   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));
@@ -187,7 +187,7 @@ class AstBuilder extends ScopeListener {
 
   void endFunctionBody(int count, Token beginToken, Token endToken) {
     debugEvent("FunctionBody");
-    List statements = popList(count);
+    List<Statement> statements = popList(count);
     if (beginToken != null) {
       exitLocalScope();
     }