Download location: better accessibility for radio button.

This CL sets a description for accessibility purpose on the radio
button in download preferences.

Bug: 850254
Change-Id: I5c854041e26094dd69cd95e74cacd06cb3eed4f4
Reviewed-on: https://chromium-review.googlesource.com/1103306Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568249}

chrome/android/java/res/layout/download_location_preference_item.xml

@@ -16,8 +16,7 @@
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_marginStart="10dp"
-        android:layout_marginEnd="6dp"
-        android:importantForAccessibility="no" />
+        android:layout_marginEnd="6dp" />
 
     <LinearLayout
         android:layout_width="0dp"

chrome/android/java/src/org/chromium/chrome/browser/preferences/download/DownloadLocationPreferenceAdapter.java

@@ -71,8 +71,16 @@ public class DownloadLocationPreferenceAdapter
 
         TextView summaryText = (TextView) view.findViewById(R.id.description);
         if (isEnabled(position)) {
-            summaryText.setText(DownloadUtils.getStringForAvailableBytes(
-                    getContext(), directoryOption.availableSpace));
+            String summary = DownloadUtils.getStringForAvailableBytes(
+                    getContext(), directoryOption.availableSpace);
+            summaryText.setText(summary);
+
+            // Build description for accessibility.
+            StringBuilder accessibilityDescription = new StringBuilder();
+            accessibilityDescription.append(directoryOption.name);
+            accessibilityDescription.append(" ");
+            accessibilityDescription.append(summary);
+            radioButton.setContentDescription(accessibilityDescription);
         } else {
             radioButton.setEnabled(false);
             titleText.setEnabled(false);