Add Crashlytics Timber.Tree

This commit logs non-fatal errors and warnings to Crashlytics in
production.

app/src/main/java/org/selfconference/android/App.java

@@ -8,6 +8,7 @@
 import dagger.ObjectGraph;
 import io.fabric.sdk.android.Fabric;
 import org.selfconference.android.data.Injector;
+import org.selfconference.android.util.CrashlyticsTree;
 import timber.log.Timber;
 import timber.log.Timber.DebugTree;
 
@@ -55,6 +56,7 @@ protected void installLeakCanary() {
   protected void setupFabric() {
     if (!BuildConfig.DEBUG) {
       Fabric.with(this, new Crashlytics());
+      Timber.plant(new CrashlyticsTree());
     }
   }
 }

app/src/main/java/org/selfconference/android/util/CrashlyticsTree.java

@@ -0,0 +1,27 @@
+package org.selfconference.android.util;
+
+import android.util.Log;
+import com.crashlytics.android.Crashlytics;
+import com.crashlytics.android.core.CrashlyticsCore;
+import timber.log.Timber;
+
+public final class CrashlyticsTree extends Timber.Tree {
+  @Override protected void log(int priority, String tag, String message, Throwable t) {
+    CrashlyticsCore crashlyticsCore = Crashlytics.getInstance().core;
+
+    crashlyticsCore.log(priority, tag, message);
+
+    if (t == null) {
+      return;
+    }
+    if (priority == Log.ERROR) {
+      crashlyticsCore.logException(t);
+    } else {
+      crashlyticsCore.log(priority, tag, Log.getStackTraceString(t));
+    }
+  }
+
+  @Override protected boolean isLoggable(int priority) {
+    return !(priority == Log.DEBUG || priority == Log.VERBOSE);
+  }
+}