Add an observer to log blocked threads.

core-util/build.gradle

@@ -1,6 +1,10 @@
-apply plugin: 'com.android.library'
-apply plugin: 'com.google.protobuf'
-apply plugin: 'witness'
+plugins {
+    id 'com.android.library'
+    id 'com.google.protobuf'
+    id 'witness'
+    id 'kotlin-android'
+    id 'kotlin-kapt'
+}
 apply from: 'witness-verifications.gradle'
 
 android {
@@ -18,6 +22,9 @@ android {
         sourceCompatibility JAVA_VERSION
         targetCompatibility JAVA_VERSION
     }
+    kotlinOptions {
+        jvmTarget = '1.8'
+    }
 }
 
 dependencyVerification {
@@ -46,6 +53,7 @@ dependencies {
 
     api libs.androidx.annotation
 
+    implementation libs.androidx.core.ktx
     implementation libs.google.protobuf.javalite
 
     testImplementation testLibs.junit.junit