Fix crash when querying a runtime config that is defined in environment

src/utils/SkRTConf.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 "SkRTConf.h"
 #include "SkOSFile.h"
 
@@ skipping 196 matching lines @@
 static inline void str_replace(char *s, char search, char replace) {
     for (char *ptr = s ; *ptr ; ptr++) {
         if (*ptr == search) {
             *ptr = replace;
         }
     }
 }
 
 template<typename T> bool SkRTConfRegistry::parse(const char *name, T* value) {
     SkString *str = NULL;
+    SkString tmp;
 
     for (int i = fConfigFileKeys.count() - 1 ; i >= 0; i--) {
         if (fConfigFileKeys[i]->equals(name)) {
             str = fConfigFileValues[i];
             break;
         }
     }
 
     SkString environment_variable("skia.");
     environment_variable.append(name);
 
     const char *environment_value = getenv(environment_variable.c_str());
     if (environment_value) {
+        if (NULL == str) {
+            str = &tmp;
+        }
         str->set(environment_value);
     } else {
         // apparently my shell doesn't let me have environment variables that
         // have periods in them, so also let the user substitute underscores.
         SkString underscore_environment_variable("skia_");
         char *underscore_name = SkStrDup(name);
         str_replace(underscore_name,'.','_');
         underscore_environment_variable.append(underscore_name);
         sk_free(underscore_name);
         environment_value = getenv(underscore_environment_variable.c_str());
         if (environment_value) {
+            if (NULL == str) {
+                str = &tmp;
+            }
             str->set(environment_value);
         }
     }
 
     if (!str) {
         return false;
     }
 
     bool success;
     T new_value = doParse<T>(str->c_str(),&success);
@@ skipping 36 matching lines @@
 template void SkRTConfRegistry::set(const char *name, int value);
 template void SkRTConfRegistry::set(const char *name, unsigned int value);
 template void SkRTConfRegistry::set(const char *name, float value);
 template void SkRTConfRegistry::set(const char *name, double value);
 template void SkRTConfRegistry::set(const char *name, char * value);
 
 SkRTConfRegistry &skRTConfRegistry() {
     static SkRTConfRegistry r;
     return r;
 }
+
+
+#ifdef SK_SUPPORT_UNITTEST
+
+#ifdef SK_BUILD_FOR_WIN32
+static void sk_setenv(const char* key, const char* value) {
+    _putenv_s(key, value);
+}
+#else
+static void sk_setenv(const char* key, const char* value) {
+    setenv(key, value, 1);
+}
+#endif
+
+void SkRTConfRegistry::UnitTest() {
+    SkRTConfRegistry registryWithoutContents(true);
+
+    sk_setenv("skia_nonexistent_item", "132");
+    int result = 0;
+    registryWithoutContents.parse("nonexistent.item", &result);
+    SkASSERT(result == 132);
+}
+
+SkRTConfRegistry::SkRTConfRegistry(bool)
+    : fConfs(100) {
+}
+#endif