Video capture Android: enable unittests for Camera2 API

media/capture/video/android/java/src/org/chromium/media/VideoCaptureCamera2.java

Index: media/capture/video/android/java/src/org/chromium/media/VideoCaptureCamera2.java
diff --git a/media/capture/video/android/java/src/org/chromium/media/VideoCaptureCamera2.java b/media/capture/video/android/java/src/org/chromium/media/VideoCaptureCamera2.java
index 3ea39967b8dfd19cd4ac613df57ed49286a9e024..d473493d0fffc483116821d9652c8dc263936599 100644
--- a/media/capture/video/android/java/src/org/chromium/media/VideoCaptureCamera2.java
+++ b/media/capture/video/android/java/src/org/chromium/media/VideoCaptureCamera2.java
@@ -401,8 +401,7 @@ public class VideoCaptureCamera2 extends VideoCapture {
         try {
             return manager.getCameraIdList().length;
         } catch (CameraAccessException | SecurityException ex) {
-            // SecurityException is an undocumented exception, but has been seen in
-            // http://crbug/605424.
+            // SecurityException is undocumented but seen in the wild: https://crbug/605424.
             Log.e(TAG, "getNumberOfCameras: getCameraIdList(): ", ex);
             return 0;
         }
@@ -530,7 +529,18 @@ public class VideoCaptureCamera2 extends VideoCapture {
         changeCameraStateAndNotify(CameraState.OPENING);
         final CameraManager manager =
                 (CameraManager) mContext.getSystemService(Context.CAMERA_SERVICE);
-        final Handler mainHandler = new Handler(mContext.getMainLooper());
+
+        Handler mainHandler = null;
+        if (!mTestMode) {
+            mainHandler = new Handler(mContext.getMainLooper());
+        } else {
+            // Usually we deliver frames on |mContext|s thread, but unit tests
+            // occupy its Looper; deliver frames on a background thread instead.
+            HandlerThread thread = new HandlerThread("CameraPicture");
+            thread.start();
+            mainHandler = new Handler(thread.getLooper());
+        }
+
         final CrStateListener stateListener = new CrStateListener();
         try {
             manager.openCamera(Integer.toString(mId), stateListener, mainHandler);