Add a unittest case of ReplaceStringPlaceholders()

base/string_util.cc

Index: base/string_util.cc
diff --git a/base/string_util.cc b/base/string_util.cc
index 1ad9abe5d8396f20dcefd5170aedf4e5644391ef..0cbb25fcb8c06354af111a6af0f2096b18e2ab2c 100644
--- a/base/string_util.cc
+++ b/base/string_util.cc
@@ -831,7 +831,6 @@ template<class FormatStringType, class OutStringType>
 OutStringType DoReplaceStringPlaceholders(const FormatStringType& format_string,
     const std::vector<OutStringType>& subst, std::vector<size_t>* offsets) {
   size_t substitutions = subst.size();
-  DCHECK(substitutions < 10);
 
   size_t sub_length = 0;
   for (typename std::vector<OutStringType>::const_iterator iter = subst.begin();
@@ -856,7 +855,14 @@ OutStringType DoReplaceStringPlaceholders(const FormatStringType& format_string,
           }
           --i;
         } else {
-          uintptr_t index = *i - '1';
+          uintptr_t index = 0;
+          while ('0' <= *i && '9' >= *i) {
+            index *= 10;
+            index += *i - '0';
+            ++i;
+          }
+          --i;
+          index -= 1;
           if (offsets) {
             ReplacementOffset r_offset(index,
                 static_cast<int>(formatted.size()));