Fix a initialization bug in BitmapRegionDecoder.

#define kClassPathName  "android/graphics/BitmapRegionDecoder"

static jclass make_globalref(JNIEnv* env, const char classname[]) {

    jclass c = env->FindClass(classname);

    SkASSERT(c);

    return (jclass)env->NewGlobalRef(c);

}

static jfieldID getFieldIDCheck(JNIEnv* env, jclass clazz,

                                const char fieldname[], const char type[]) {

    jfieldID id = env->GetFieldID(clazz, fieldname, type);

    SkASSERT(id);

    return id;

}

int register_android_graphics_BitmapRegionDecoder(JNIEnv* env);

int register_android_graphics_BitmapRegionDecoder(JNIEnv* env)

{

    gFileDescriptor_class = make_globalref(env, "java/io/FileDescriptor");

    gFileDescriptor_descriptor = getFieldIDCheck(env, gFileDescriptor_class, "descriptor", "I");

    return android::AndroidRuntime::registerNativeMethods(env, kClassPathName,

            gBitmapRegionDecoderMethods, SK_ARRAY_COUNT(gBitmapRegionDecoderMethods));

}