Make various string_util functions take StringPieces instead of char[].

extensions/common/permissions/socket_permission_entry.cc

Index: extensions/common/permissions/socket_permission_entry.cc
diff --git a/extensions/common/permissions/socket_permission_entry.cc b/extensions/common/permissions/socket_permission_entry.cc
index ddadf22c4e6d4eae77063de2a5e5d0c6b05a024f..ba409c58f149c7d9cf9dbb8fb94e0604e6743f6a 100644
--- a/extensions/common/permissions/socket_permission_entry.cc
+++ b/extensions/common/permissions/socket_permission_entry.cc
@@ -28,11 +28,8 @@ const int kWildcardPortNumber = 0;
 const int kInvalidPort = -1;
 
 bool StartsOrEndsWithWhitespace(const std::string& str) {
-  if (str.find_first_not_of(base::kWhitespaceASCII) != 0)
-    return true;
-  if (str.find_last_not_of(base::kWhitespaceASCII) != str.length() - 1)
-    return true;
-  return false;
+  return !str.empty() &&
+      (IsWhitespace(str[0]) || IsWhitespace(str[str.length() - 1]));
 }
 
 }  // namespace