Auto Exposure:

  - Filter results down to the three best.
  - Changing exposure based on distance to the target or at random.
  - Plumb exposure through the debug framework.
  - Refactor into target finder.

Change-Id: Ia083f56859938bf0825472fd15d248c545f6f2fc
diff --git a/aos/vision/debug/debug_framework.cc b/aos/vision/debug/debug_framework.cc
index 1d94217..7b3ad76 100644
--- a/aos/vision/debug/debug_framework.cc
+++ b/aos/vision/debug/debug_framework.cc
@@ -60,6 +60,11 @@
     if (GetScreenHeight() < 1024) {
       view_.SetScale(1.0);
     }
+
+    // Pass along the set exposure so that users can acceess it.
+    filter->InstallSetExposure([this](uint32_t abs_exp) {
+        this->SetExposure(abs_exp);
+    });
   }
 
   // This the first stage in the pipeline that takes