Fail CachingTest if our weak reference is never cleared.

We're waiting for a specific condition that should occur, but it's
dependent on the VM. I haven't seen it fail with 100 attempts, but it's
possible it might. Failing with a specific assertion should make it
easier to distinguish between failed tests and flakes.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177625844

instrumentation/src/androidTest/java/com/bumptech/glide/CachingTest.java

@@ -118,6 +118,7 @@ public void run() {
     // Wait for the weak reference to be cleared and the request to be removed from active
     // resources.
     // De-flake by allowing multiple tries
+    boolean isWeakRefCleared = false;
     for (int j = 0; j < 100; j++) {
       Runtime.getRuntime().gc();
       concurrency.pokeMainThread();
@@ -135,10 +136,15 @@ public void run() {
         GlideApp.with(context).clear(target);
       } catch (RuntimeException e) {
         // The item has been cleared from active resources.
+        isWeakRefCleared = true;
         break;
       }
     }
 
+    if (!isWeakRefCleared) {
+      fail("Failed to clear weak ref.");
+    }
+
     concurrency.get(
         GlideApp.with(context)
             .load(ResourceIds.raw.canonical)