Have external resource call init() explicitly.

Change-Id: Ibdd444478d0d171353a58c060022f5a181f9d1c4
Flag: TEST_ONLY
Test: go/testedequals
Bug: 230027385

tests/multivalentTests/src/com/android/launcher3/util/SandboxApplication.kt

@@ -73,9 +73,7 @@ class SandboxApplication private constructor(private val base: SandboxApplicatio
 
     override fun apply(statement: Statement, description: Description): Statement {
         return object : ExternalResource() {
-                override fun before() {
-                    base.app = this@SandboxApplication
-                }
+                override fun before() = init()
 
                 override fun after() = onDestroy()
             }