Fix a bug that could occur when converting strings with leading characters above 127.

BUG=None
TEST=base_unittests --gtest_filter=*StringToInt*

Review URL: http://codereview.chromium.org/4129012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@64789 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/string_number_conversions.cc b/base/string_number_conversions.cc
index 488d8075..76158dee 100644
--- a/base/string_number_conversions.cc
+++ b/base/string_number_conversions.cc
@@ -143,7 +143,7 @@
 template<> class WhitespaceHelper<char> {
  public:
   static bool Invoke(char c) {
-    return 0 != isspace(c);
+    return 0 != isspace(static_cast<unsigned char>(c));
   }
 };