Fix the build.

tools/flags/SkCommandLineFlags.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCommandLineFlags.h"
 #include "SkTDArray.h"
 
 bool SkFlagInfo::CreateStringFlag(const char* name, const char* shortName,
                                   SkCommandLineFlags::StringArray* pStrings,
                                   const char* defaultValue, const char* helpString) {
     SkFlagInfo* info = SkNEW_ARGS(SkFlagInfo, (name, shortName, kString_FlagType, helpString));
     info->fDefaultString.set(defaultValue);
 
     info->fStrings = pStrings;
     SetDefaultStrings(pStrings, defaultValue);
     return true;
 }
 
 void SkFlagInfo::SetDefaultStrings(SkCommandLineFlags::StringArray* pStrings,
                                    const char* defaultValue) {
     pStrings->reset();
+    if (NULL == defaultValue) {
+        return;
+    }
     // If default is "", leave the array empty.
     size_t defaultLength = strlen(defaultValue);
     if (defaultLength > 0) {
         const char* const defaultEnd = defaultValue + defaultLength;
         const char* begin = defaultValue;
         while (true) {
             while (begin < defaultEnd && ' ' == *begin) {
                 begin++;
             }
             if (begin < defaultEnd) {
@@ skipping 258 matching lines @@
     gHead = NULL;
     while (flag != NULL) {
         SkFlagInfo* next = flag->next();
         SkDELETE(flag);
         flag = next;
     }
     if (helpPrinted) {
         exit(0);
     }
 }