[Cronet] Make BrotliTest install test files before using them

This prevents failures to find these files.

Change-Id: I60f7c3bd3f7a20142d4758dc5dd9b0944ded79a6
Reviewed-on: https://chromium-review.googlesource.com/575276Reviewed-by: Helen Li <xunjieli@chromium.org>
Commit-Queue: Paul Jensen <pauljensen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487653}

components/cronet/android/test/javatests/src/org/chromium/net/BrotliTest.java

@@ -19,6 +19,7 @@ public class BrotliTest extends CronetTestBase {
     @Override
     protected void setUp() throws Exception {
         super.setUp();
+        TestFilesInstaller.installIfNeeded(getContext());
         assertTrue(Http2TestServer.startHttp2TestServer(
                 getContext(), SERVER_CERT_PEM, SERVER_KEY_PKCS8_PEM));
     }