Camera2: Add flush support

- On HAL2 devices, fall back to wait until idle
- On HAL3 devices, call HAL flush method

Bug: 9758581
Change-Id: Ie1c570a15f6590a1ee6c271e3b989c48079b468a
diff --git a/services/camera/libcameraservice/device2/Camera2Device.h b/services/camera/libcameraservice/device2/Camera2Device.h
index 8945ec2..2aa22a2 100644
--- a/services/camera/libcameraservice/device2/Camera2Device.h
+++ b/services/camera/libcameraservice/device2/Camera2Device.h
@@ -67,6 +67,8 @@
     virtual status_t triggerPrecaptureMetering(uint32_t id);
     virtual status_t pushReprocessBuffer(int reprocessStreamId,
             buffer_handle_t *buffer, wp<BufferReleasedListener> listener);
+    // Flush implemented as just a wait
+    virtual status_t flush();
   private:
     const int mId;
     camera2_device_t *mHal2Device;
@@ -113,6 +115,9 @@
         status_t setStreamSlot(camera_metadata_t *buf);
         status_t setStreamSlot(const List<camera_metadata_t*> &bufs);
 
+        // Clear the request queue and the streaming slot
+        status_t clear();
+
         status_t dump(int fd, const Vector<String16>& args);
 
       private: