[android] Fix running native-tests on Android 10.

Explicitly turn on requestLegacyExternalStorage attribute for native
tests, since it is disabled by default on Android 10. The storage access
is needed for listing the tests in a test-suite.

BUG=none

Change-Id: I5f6a399dec50204e47aa4c162ede1a9f64111cf4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2567713Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Auto-Submit: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832415}

testing/android/native_test/java/AndroidManifest.xml.jinja2

@@ -22,7 +22,13 @@ found in the LICENSE file.
     <uses-permission android:name="android.permission.WAKE_LOCK"/>
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
 
+    <!-- Explicitly set the attribute requestLegacyExternalStorage to "true"
+         since it is "false" by default on apps targeting Android 10, and that
+         breaks test listing. See
+         https://developer.android.com/training/data-storage#scoped-storage and
+         https://developer.android.com/training/data-storage/compatibility. -->
     <application android:label="NativeTests"
+            android:requestLegacyExternalStorage="true"
             android:name="org.chromium.native_test.NativeTestApplication">
         <uses-library android:name="android.test.runner"/>
         {% if use_native_activity == 'true' %}