Add logging for why Lightbringer upgrading is not available

This will be very helpful when troubleshooting issues with upgrades

Because logging this is very spammy, I am logging the messages as verbose instead of info level. This means they will not be in bug reports, but at least we on Dialer and other teams working on Duo integration can flip them on to debug locally.

Test: existing tests
PiperOrigin-RevId: 166879801
Change-Id: Ideb660efc7b4f7cf90767b4fd43bb997008d3378
diff --git a/java/com/android/incallui/videotech/lightbringer/LightbringerTech.java b/java/com/android/incallui/videotech/lightbringer/LightbringerTech.java
index 26d6347..4882ba8 100644
--- a/java/com/android/incallui/videotech/lightbringer/LightbringerTech.java
+++ b/java/com/android/incallui/videotech/lightbringer/LightbringerTech.java
@@ -23,6 +23,7 @@
 import android.telecom.Call;
 import com.android.contacts.common.compat.telecom.TelecomManagerCompat;
 import com.android.dialer.common.Assert;
+import com.android.dialer.common.LogUtil;
 import com.android.dialer.configprovider.ConfigProviderBindings;
 import com.android.dialer.lightbringer.Lightbringer;
 import com.android.dialer.lightbringer.LightbringerListener;
@@ -54,11 +55,33 @@
 
   @Override
   public boolean isAvailable(Context context) {
-    return Build.VERSION.SDK_INT >= Build.VERSION_CODES.O
-        && ConfigProviderBindings.get(context).getBoolean("enable_lightbringer_video_upgrade", true)
-        && callState == Call.STATE_ACTIVE
-        && lightbringer.supportsUpgrade(context, callingNumber)
-        && TelecomManagerCompat.supportsHandover();
+    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
+      LogUtil.v("LightbringerTech.isAvailable", "upgrade unavailable, only supported on O+");
+      return false;
+    }
+
+    if (!ConfigProviderBindings.get(context)
+        .getBoolean("enable_lightbringer_video_upgrade", true)) {
+      LogUtil.v("LightbringerTech.isAvailable", "upgrade disabled by flag");
+      return false;
+    }
+
+    if (callState != Call.STATE_ACTIVE) {
+      LogUtil.v("LightbringerTech.isAvailable", "upgrade unavailable, call must be active");
+      return false;
+    }
+
+    if (!TelecomManagerCompat.supportsHandover()) {
+      LogUtil.v("LightbringerTech.isAvailable", "upgrade unavailable, telephony support missing");
+      return false;
+    }
+
+    if (!lightbringer.supportsUpgrade(context, callingNumber)) {
+      LogUtil.v("LightbringerTech.isAvailable", "upgrade unavailable, number does not support it");
+      return false;
+    }
+
+    return true;
   }
 
   @Override