Avoid unnecessary FindClass("java/lang/String").

Use previously retrieved global reference instead.
Check for NULL after creating the global reference.

Change-Id: I21670d2ef0f63ddb5801dd21e7e56359e5519479
diff --git a/core/jni/android_util_AssetManager.cpp b/core/jni/android_util_AssetManager.cpp
index d422951..89dc70d 100644
--- a/core/jni/android_util_AssetManager.cpp
+++ b/core/jni/android_util_AssetManager.cpp
@@ -293,17 +293,10 @@
         return NULL;
     }
 
-    jclass cls = env->FindClass("java/lang/String");
-    LOG_FATAL_IF(cls == NULL, "No string class?!?");
-    if (cls == NULL) {
-        delete dir;
-        return NULL;
-    }
-
     size_t N = dir->getFileCount();
 
     jobjectArray array = env->NewObjectArray(dir->getFileCount(),
-                                                cls, NULL);
+                                                g_stringClass, NULL);
     if (array == NULL) {
         delete dir;
         return NULL;
@@ -1455,19 +1448,13 @@
     }
     const ResTable& res(am->getResources());
 
-    jclass cls = env->FindClass("java/lang/String");
-    LOG_FATAL_IF(cls == NULL, "No string class?!?");
-    if (cls == NULL) {
-        return NULL;
-    }
-
     const ResTable::bag_entry* startOfBag;
     const ssize_t N = res.lockBag(arrayResId, &startOfBag);
     if (N < 0) {
         return NULL;
     }
 
-    jobjectArray array = env->NewObjectArray(N, cls, NULL);
+    jobjectArray array = env->NewObjectArray(N, g_stringClass, NULL);
     if (env->ExceptionCheck()) {
         res.unlockBag(startOfBag);
         return NULL;
@@ -1764,6 +1751,7 @@
     jclass stringClass = env->FindClass("java/lang/String");
     LOG_FATAL_IF(stringClass == NULL, "Unable to find class java/lang/String");
     g_stringClass = (jclass)env->NewGlobalRef(stringClass);
+    LOG_FATAL_IF(g_stringClass == NULL, "Unable to create global reference for class java/lang/String");
 
     return AndroidRuntime::registerNativeMethods(env,
             "android/content/res/AssetManager", gAssetManagerMethods, NELEM(gAssetManagerMethods));