Enable auto-focus on Camera2.

webrtc/api/android/java/src/org/webrtc/Camera2Session.java

Index: webrtc/api/android/java/src/org/webrtc/Camera2Session.java
diff --git a/webrtc/api/android/java/src/org/webrtc/Camera2Session.java b/webrtc/api/android/java/src/org/webrtc/Camera2Session.java
index 65c649137e849fa85bdec1ce644ce3d0efd8241b..cc99e2e26ab3743fb1f6ac30ae83af2ea957dde8 100644
--- a/webrtc/api/android/java/src/org/webrtc/Camera2Session.java
+++ b/webrtc/api/android/java/src/org/webrtc/Camera2Session.java
@@ -169,6 +169,7 @@ public class Camera2Session implements CameraSession {
             CaptureRequest.CONTROL_AE_MODE_ON);
         captureRequestBuilder.set(CaptureRequest.CONTROL_AE_LOCK, false);
         chooseStabilizationMode(captureRequestBuilder);
+        chooseFocusMode(captureRequestBuilder);
 
         captureRequestBuilder.addTarget(surface);
         session.setRepeatingRequest(
@@ -253,6 +254,20 @@ public class Camera2Session implements CameraSession {
       }
       Logging.d(TAG, "Stabilization not available.");
     }
+
+    private void chooseFocusMode(CaptureRequest.Builder captureRequestBuilder) {
+      final int[] availableFocusModes = cameraCharacteristics.get(
+          CameraCharacteristics.CONTROL_AF_AVAILABLE_MODES);
+      for (int mode : availableFocusModes) {
+        if (mode == CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_VIDEO) {
+          captureRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
+              CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_VIDEO);
+          Logging.d(TAG, "Using continuous video auto-focus.");
+          return;
+        }
+      }
+      Logging.d(TAG, "Auto-focus is not available.");
+    }
   }
 
   private class CameraCaptureCallback extends CameraCaptureSession.CaptureCallback {