Revert of Disable LayerTreeHostTestDeferCommits since it is flaky on Win....

Revert of Disable LayerTreeHostTestDeferCommits since it is flaky on Win. (patchset #2 id:20001 of https://codereview.chromium.org/864313004/)

Reason for revert:
found culprit and reverting

Original issue's description:
> Disable LayerTreeHostTestDeferCommits since it is flaky on Win.
>
> Sorry if I disabled too many tests...
>
> BUG=453787
> TBR=danakj@chromium.org
>
> Committed: https://chromium.googlesource.com/chromium/src/+/8bf8e0bde343027f98f9496e2ccc224ea418b835

TBR=perkj@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=453787

Review URL: https://codereview.chromium.org/888063002

Cr-Commit-Position: refs/heads/master@{#313940}

cc/trees/layer_tree_host_unittest.cc

@@ -2065,10 +2065,7 @@ class LayerTreeHostTestDeferCommits : public LayerTreeHostTest {
   int num_complete_commits_;
 };
 
-#if !defined(OS_WIN)
-// Flaky on Win: crbug/453787.
 SINGLE_AND_MULTI_THREAD_TEST_F(LayerTreeHostTestDeferCommits);
-#endif
 
 class LayerTreeHostWithProxy : public LayerTreeHost {
  public: