[Android] Mock AndroidSyncSettings before starting activity in SyncTestRule

This CL reorders calls in SyncTestRule so AndroidSyncSettings instance
is overridden before activity is started. This is done to prevent
classes initialized during activity initialization from grabbing
a reference to the default AndroidSyncSettings.

Bug: 903657, 903658, 906188, 906193, 906788
Change-Id: Ib412d7748a8ec6f48b80436051a932d6b7713940
Reviewed-on: https://chromium-review.googlesource.com/c/1356583Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612637}

chrome/android/javatests/src/org/chromium/chrome/browser/sync/SyncTestRule.java

@@ -219,11 +219,11 @@ public class SyncTestRule extends ChromeActivityTestRule<ChromeActivity> {
         final Statement base = super.apply(new Statement() {
             @Override
             public void evaluate() throws Throwable {
+                setUpMockAndroidSyncSettings();
+
                 startMainActivityForSyncTest();
                 mContext = InstrumentationRegistry.getTargetContext();
 
-                setUpMockAndroidSyncSettings();
-
                 ThreadUtils.runOnUiThreadBlocking(new Runnable() {
                     @Override
                     public void run() {