[Android] Avoid unnecessary JNI calls for empty string conversions

base/android/jni_string_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/android/jni_string.h"
 
 #include "base/android/jni_android.h"
 #include "base/android/scoped_java_ref.h"
 #include "base/strings/utf_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 10 matching lines @@
 }
 
 TEST(JniString, BasicConversionsUTF16) {
   const string16 kSimpleString = UTF8ToUTF16("SimpleTest16");
   JNIEnv* env = AttachCurrentThread();
   string16 result =
       ConvertJavaStringToUTF16(ConvertUTF16ToJavaString(env, kSimpleString));
   EXPECT_EQ(kSimpleString, result);
 }
 
+TEST(JniString, EmptyConversionUTF8) {
+  const std::string kEmptyString = "";
+  JNIEnv* env = AttachCurrentThread();
+  std::string result =
+      ConvertJavaStringToUTF8(ConvertUTF8ToJavaString(env, kEmptyString));
+  EXPECT_EQ(kEmptyString, result);
+}
+
+TEST(JniString, EmptyConversionUTF16) {
+  const string16 kEmptyString = UTF8ToUTF16("");
+  JNIEnv* env = AttachCurrentThread();
+  string16 result =
+      ConvertJavaStringToUTF16(ConvertUTF16ToJavaString(env, kEmptyString));
+  EXPECT_EQ(kEmptyString, result);
+}
+
 }  // namespace android
 }  // namespace base