pt 1 in reviving the android build (copied from pm 28a1, wish me luck)

mobile/android/base/java/org/mozilla/gecko/ScreenshotObserver.java

@@ -0,0 +1,146 @@
+/* -*- Mode: Java; c-basic-offset: 4; tab-width: 4; indent-tabs-mode: nil; -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko;
+
+import org.mozilla.gecko.AppConstants.Versions;
+import org.mozilla.gecko.permissions.Permissions;
+import org.mozilla.gecko.util.ThreadUtils;
+
+import android.Manifest;
+import android.content.ContentResolver;
+import android.content.Context;
+import android.database.ContentObserver;
+import android.database.Cursor;
+import android.net.Uri;
+import android.provider.MediaStore;
+import android.util.Log;
+
+public class ScreenshotObserver {
+    private static final String LOGTAG = "GeckoScreenshotObserver";
+    public Context context;
+
+    /**
+     * Listener for screenshot changes.
+     */
+    public interface OnScreenshotListener {
+        /**
+         * This callback is executed on the UI thread.
+         */
+        public void onScreenshotTaken(String data, String title);
+    }
+
+    private OnScreenshotListener listener;
+
+    public ScreenshotObserver() {
+    }
+
+    public void setListener(Context context, OnScreenshotListener listener) {
+        this.context = context;
+        this.listener = listener;
+    }
+
+    private MediaObserver mediaObserver;
+    private String[] mediaProjections = new String[] {
+                    MediaStore.Images.ImageColumns.DATA,
+                    MediaStore.Images.ImageColumns.DISPLAY_NAME,
+                    MediaStore.Images.ImageColumns.BUCKET_DISPLAY_NAME,
+                    MediaStore.Images.ImageColumns.DATE_TAKEN,
+                    MediaStore.Images.ImageColumns.TITLE
+    };
+
+    /**
+     * Start ScreenshotObserver if this device is supported and all required runtime permissions
+     * have been granted by the user. Calling this method will not prompt for permissions.
+     */
+    public void start() {
+        Permissions.from(context)
+                   .withPermissions(Manifest.permission.WRITE_EXTERNAL_STORAGE)
+                   .doNotPrompt()
+                   .run(startObserverRunnable());
+    }
+
+    private Runnable startObserverRunnable() {
+        return new Runnable() {
+            @Override
+            public void run() {
+                try {
+                    if (mediaObserver == null) {
+                        mediaObserver = new MediaObserver();
+                        context.getContentResolver().registerContentObserver(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, false, mediaObserver);
+                    }
+                } catch (Exception e) {
+                    Log.e(LOGTAG, "Failure to start watching media: ", e);
+                }
+            }
+        };
+    }
+
+    public void stop() {
+        if (mediaObserver == null) {
+            return;
+        }
+
+        try {
+            context.getContentResolver().unregisterContentObserver(mediaObserver);
+            mediaObserver = null;
+        } catch (Exception e) {
+            Log.e(LOGTAG, "Failure to stop watching media: ", e);
+        }
+    }
+
+    public void onMediaChange(final Uri uri) {
+        // Make sure we are on not on the main thread.
+        final ContentResolver cr = context.getContentResolver();
+        ThreadUtils.postToBackgroundThread(new Runnable() {
+            @Override
+            public void run() {
+                // Find the most recent image added to the MediaStore and see if it's a screenshot.
+                final Cursor cursor = cr.query(uri, mediaProjections, null, null, MediaStore.Images.ImageColumns.DATE_ADDED + " DESC LIMIT 1");
+                try {
+                    if (cursor == null) {
+                        return;
+                    }
+
+                    while (cursor.moveToNext()) {
+                        String data = cursor.getString(0);
+                        Log.i(LOGTAG, "data: " + data);
+                        String display = cursor.getString(1);
+                        Log.i(LOGTAG, "display: " + display);
+                        String album = cursor.getString(2);
+                        Log.i(LOGTAG, "album: " + album);
+                        long date = cursor.getLong(3);
+                        String title = cursor.getString(4);
+                        Log.i(LOGTAG, "title: " + title);
+                        if (album != null && album.toLowerCase().contains("screenshot")) {
+                            if (listener != null) {
+                                listener.onScreenshotTaken(data, title);
+                                break;
+                            }
+                        }
+                    }
+                } catch (Exception e) {
+                    Log.e(LOGTAG, "Failure to process media change: ", e);
+                } finally {
+                    if (cursor != null) {
+                        cursor.close();
+                    }
+                }
+            }
+        });
+    }
+
+    private class MediaObserver extends ContentObserver {
+        public MediaObserver() {
+            super(null);
+        }
+
+        @Override
+        public void onChange(boolean selfChange) {
+            super.onChange(selfChange);
+            onMediaChange(MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
+        }
+    }
+}