Test large inputs for sha1 and sha256, also remove unused import.

BUG=
R=rmacnak@google.com

Review URL: https://codereview.chromium.org//1348823004 .

lib/src/hash_base.dart

@@ -4,7 +4,6 @@
 
 library crypto.hash_base;
 
-import 'dart:math' as math;
 import 'dart:typed_data';
 
 import 'hash.dart';

test/sha1_test.dart

@@ -7,6 +7,7 @@ library sha1_test;
 
 import "package:crypto/crypto.dart";
 import "package:test/test.dart";
+import 'very_long_input.dart';
 
 part 'sha1_long_test_vectors.dart';
 part 'sha1_short_test_vectors.dart';
@@ -21,6 +22,10 @@ void main() {
   test('short inputs', () {
     _testStandardVectors(sha1_short_inputs, sha1_short_mds);
   });
+  test('input bit length greater than 32 bits', () {
+    veryLongInput(
+        new SHA1(), 1000000000, '1dd775261d7abab0b66910acc1d827a2c3799eaf');
+  });
 }
 
 void _testExpectedValues() {

test/sha256_test.dart

@@ -7,6 +7,7 @@ library sha256_test;
 
 import "package:test/test.dart";
 import "package:crypto/crypto.dart";
+import 'very_long_input.dart';
 
 part 'sha256_long_test_vectors.dart';
 part 'sha256_short_test_vectors.dart';
@@ -19,6 +20,10 @@ void main() {
       () => _testStandardVectors(sha256_long_inputs, sha256_long_mds));
   test('short inputs',
       () => _testStandardVectors(sha256_short_inputs, sha256_short_mds));
+  test('input bit length greater than 32 bits', () {
+    veryLongInput(new SHA256(), 1000000000,
+        'bc17f06f9d9b5f6f79ca189a1772b1a3a38d6e40c45bec50f9c4f28144efddca');
+  });
 }
 
 void _testExpectedValues() {

test/very_long_input.dart

@@ -0,0 +1,14 @@
+library very_long_input_test;
+
+import 'package:crypto/crypto.dart';
+import 'package:test/test.dart';
+
+veryLongInput(digester, int byteLength, String verify) {
+  var nullCharacter = '\u0000'.codeUnitAt(0);
+  var input = [nullCharacter];
+  for (var i = 0; i < byteLength; i++) {
+    digester.add(input);
+  }
+  var d = digester.close();
+  expect(CryptoUtils.bytesToHex(d), verify);
+}