Revert "Disable test FrameTreeTest.FindFrames"

This reverts commit 1c854a22.

Reason for revert: Failures were not due to this test.  Passes locally.

Original change's description:
> Disable test FrameTreeTest.FindFrames
> 
> Test FrameTreeTest.FindFrames is flaky. Disable it.
> 
> TBR=creis@chromium.org
> 
> Bug: 826599
> Change-Id: I3536ef001db9f8df4193ad7c709cc4f7c4246d97
> Reviewed-on: https://chromium-review.googlesource.com/985996
> Reviewed-by: Adam Rice <ricea@chromium.org>
> Commit-Queue: Adam Rice <ricea@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#546808}

TBR=creis@chromium.org,ricea@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 826599
Change-Id: I1b3aeeaccb8458fc57959efdf236d126280cde5b
Reviewed-on: https://chromium-review.googlesource.com/990752Reviewed-by: Charlie Reis <creis@chromium.org>
Commit-Queue: Charlie Reis <creis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547545}

content/browser/frame_host/frame_tree_unittest.cc

-// Copyright 2013 The Chromium Authors. All rights reserved.
+// Copyright 2013 The Chromium Authors.All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -310,8 +310,7 @@ TEST_F(FrameTreeTest, Shape) {
 }
 
 // Ensure frames can be found by frame_tree_node_id, routing ID, or name.
-// Disabled due to flakiness: http://crbug.com/826599
-TEST_F(FrameTreeTest, DISABLED_FindFrames) {
+TEST_F(FrameTreeTest, FindFrames) {
   main_test_rfh()->InitializeRenderFrameIfNeeded();
 
   // Add a few child frames to the main frame.