cc: Speculative fix for texture layer visibility change test

Not resetting the |resource_changed_| flag will cause the same resource
to be returned if multiple calls to PrepareTransferableResource() are
made, and this triggers a DCHECK failure in TextureLayer.

Bug: 1114952
Change-Id: I6b3b6ff00fd32316d67bee46f4e45f7bdd418a23
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2548520Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829317}

cc/layers/texture_layer_unittest.cc

@@ -1004,6 +1004,7 @@ class TextureLayerChangeInvisibleMailboxTest
     ++prepare_called_;
     if (!resource_changed_)
       return false;
+    resource_changed_ = false;
     *resource = resource_;
     *release_callback = viz::SingleReleaseCallback::Create(base::BindOnce(
         &TextureLayerChangeInvisibleMailboxTest::ResourceReleased,