[Android] Avoid unnecessary JNI calls for empty string conversions

base/android/jni_string_unittest.cc

Index: base/android/jni_string_unittest.cc
diff --git a/base/android/jni_string_unittest.cc b/base/android/jni_string_unittest.cc
index abd0683170e514d2e705d4f899a72be1df7f5783..3da8b870e6649bfc4140ef2881fe21a30c205471 100644
--- a/base/android/jni_string_unittest.cc
+++ b/base/android/jni_string_unittest.cc
@@ -28,5 +28,21 @@ TEST(JniString, BasicConversionsUTF16) {
   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