Use debug apks for dev builds.

shell/android/apk/AndroidManifest.xml.jinja2

 <?xml version="1.0" encoding="utf-8"?>
 
 <!-- Copyright 2013 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.
  -->
 
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="{{ manifest_package }}"
     android:versionCode="{{ version_code }}"
     android:versionName="{{ version_name }}">
 
     <uses-sdk android:minSdkVersion="14" android:targetSdkVersion="23" />
     <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
     <uses-permission android:name="android.permission.ACCESS_NETWORK_CONDITIONS"/>
     <uses-permission android:name="android.permission.CAMERA" />
     <uses-permission android:name="android.permission.INTERNET"/>
     <uses-permission android:name="android.permission.NFC"/>
     <uses-permission android:name="android.permission.READ_CONTACTS" />
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
     <uses-permission android:name="android.permission.RECORD_AUDIO"/>
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
 
     <application android:icon="@mipmap/ic_launcher"
             android:name="org.chromium.mojo.shell.MojoShellApplication"
-            android:label="{{ apk_name }}">
+            android:label="{{ apk_name }}"
+            android:debuggable="{{ debuggable }}">
         <meta-data android:name="com.google.android.gms.version"
                    android:value="@integer/google_play_services_version" />
         <activity android:name="org.chromium.mojo.shell.MojoShellActivity"
                   android:launchMode="standard"
                   android:documentLaunchMode="none"
                   android:theme="@style/Theme.Transparent">
             <intent-filter>
                 <!-- A mojo://host/path url will load the app at the
                      https://host/path URL.
                  -->
@@ skipping 26 matching lines @@
                 <data android:mimeType="text/plain"/>
             </intent-filter>
         </activity>
         <activity android:name="org.chromium.mojo.shell.IntentReceiverActivity"
                   android:theme="@style/Theme.Transparent">
         </activity>
         <service android:name="org.chromium.mojo.shell.ShellService" />
     </application>
 
 </manifest>