Enable disk cache in testHostCachePersistence

This fixes the flake.

BUG=740207

Change-Id: I68fd807c8bb9effc1c0e9e15e744146c4b1f15c0
Reviewed-on: https://chromium-review.googlesource.com/574571
Reviewed-by: Misha Efimov <mef@chromium.org>
Commit-Queue: Miriam Gershenson <mgersh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487113}
diff --git a/components/cronet/android/test/javatests/src/org/chromium/net/ExperimentalOptionsTest.java b/components/cronet/android/test/javatests/src/org/chromium/net/ExperimentalOptionsTest.java
index bd62295..c16d3e8 100644
--- a/components/cronet/android/test/javatests/src/org/chromium/net/ExperimentalOptionsTest.java
+++ b/components/cronet/android/test/javatests/src/org/chromium/net/ExperimentalOptionsTest.java
@@ -156,7 +156,8 @@
         String testHost = "host-cache-test-host";
         String testUrl = new URL("http", testHost, realPort, javaUrl.getPath()).toString();
 
-        mBuilder.setStoragePath(getTestStorage(getContext()));
+        mBuilder.setStoragePath(getTestStorage(getContext()))
+                .enableHttpCache(CronetEngine.Builder.HTTP_CACHE_DISK, 0);
 
         // Set a short delay so the pref gets written quickly.
         JSONObject staleDns = new JSONObject()
@@ -182,9 +183,7 @@
         assertNull(callback.mError);
         assertEquals(200, callback.mResponseInfo.getHttpStatusCode());
 
-        // First wait a little longer for the write to prefs to go through. Then shut down the
-        // context, persisting contents to disk, and build a new one.
-        Thread.sleep(100);
+        // Shut down the context, persisting contents to disk, and build a new one.
         context.shutdown();
         context = (CronetUrlRequestContext) mBuilder.build();