Use "languageTag" in RichInputMethodSubtype.

With this CL, RichInputMethodSubtype#getLocale() starts returning
a Locale object that is initialized with "languageTag" when it is
specified.  No behavior change is intended when "languageTag" attribute
is not available or specified.

Bug: 22858221
Change-Id: I23f2e479b8e284ce589c6950b071ba84c5dd8ce1

java/src/com/android/inputmethod/compat/InputMethodSubtypeCompatUtils.java

@@ -17,14 +17,17 @@
 package com.android.inputmethod.compat;
 
 import android.os.Build;
+import android.text.TextUtils;
 import android.view.inputmethod.InputMethodSubtype;
 
 import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.latin.RichInputMethodSubtype;
 import com.android.inputmethod.latin.common.Constants;
+import com.android.inputmethod.latin.common.LocaleUtils;
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Method;
+import java.util.Locale;
 
 import javax.annotation.Nonnull;
 
@@ -78,6 +81,21 @@ public final class InputMethodSubtypeCompatUtils {
                 || subtype.containsExtraValueKey(Constants.Subtype.ExtraValue.ASCII_CAPABLE);
     }
 
+    // Note that InputMethodSubtype.getLanguageTag() is expected to be available in Android N+.
+    private static final Method GET_LANGUAGE_TAG =
+            CompatUtils.getMethod(InputMethodSubtype.class, "getLanguageTag");
+
+    public static Locale getLocaleObject(final InputMethodSubtype subtype) {
+        // Locale.forLanguageTag() is available only in Android L and later.
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+            final String languageTag = (String) CompatUtils.invoke(subtype, null, GET_LANGUAGE_TAG);
+            if (!TextUtils.isEmpty(languageTag)) {
+                return Locale.forLanguageTag(languageTag);
+            }
+        }
+        return LocaleUtils.constructLocaleFromString(subtype.getLocale());
+    }
+
     @UsedForTesting
     public static boolean isAsciiCapableWithAPI(final InputMethodSubtype subtype) {
         return (Boolean)CompatUtils.invoke(subtype, false, METHOD_isAsciiCapable);

java/src/com/android/inputmethod/latin/RichInputMethodSubtype.java

@@ -47,7 +47,7 @@ public class RichInputMethodSubtype {
 
     public RichInputMethodSubtype(@Nonnull final InputMethodSubtype subtype) {
         mSubtype = subtype;
-        mLocale = LocaleUtils.constructLocaleFromString(mSubtype.getLocale());
+        mLocale = InputMethodSubtypeCompatUtils.getLocaleObject(mSubtype);
     }
 
     // Extra values are determined by the primary subtype. This is probably right, but