Clean up MetricsService unit test.

chrome/browser/metrics/metrics_service_unittest.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/browser/metrics/metrics_service.h"
 
+#include <ctype.h>
 #include <string>
 
-#include "base/base64.h"
-
+#include "chrome/browser/metrics/metrics_service.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-class MetricsServiceTest : public ::testing::Test {
-};
-
 // Ensure the ClientId is formatted as expected.
 TEST(MetricsServiceTest, ClientIdCorrectlyFormatted) {
   std::string clientid = MetricsService::GenerateClientID();
   EXPECT_EQ(36U, clientid.length());
-  std::string hexchars = "0123456789ABCDEF";
-  for (uint32 i = 0; i < clientid.length(); i++) {
-    char current = clientid.at(i);
-    if (i == 8 || i == 13 || i == 18 || i == 23) {
+
+  for (size_t i = 0; i < clientid.length(); ++i) {
+    char current = clientid[i];
+    if (i == 8 || i == 13 || i == 18 || i == 23)
       EXPECT_EQ('-', current);
-    } else {
-      EXPECT_TRUE(std::string::npos != hexchars.find(current));
-    }
+    else
+      EXPECT_TRUE(isxdigit(current));
   }
 }
 
 TEST(MetricsServiceTest, IsPluginProcess) {
   EXPECT_TRUE(
       MetricsService::IsPluginProcess(content::PROCESS_TYPE_PLUGIN));
   EXPECT_TRUE(
       MetricsService::IsPluginProcess(content::PROCESS_TYPE_PPAPI_PLUGIN));
   EXPECT_FALSE(
       MetricsService::IsPluginProcess(content::PROCESS_TYPE_GPU));
 }