Disable Compositor:DidFailToInitializeLayerTreeFrameSink NOTREACHED

One third of CQ runs of mash_browser_tests are failing when hitting the
NOTREACHED in Compositor:DidFailToInitializeLayerTreeFrameSink so I'm disabling
it while the cause is researched.

TBR=sadrul@chromium.org

TEST: mash_browser_tests
Bug: 742966, 743028
Change-Id: I9363ebfbdeac594d26696b5426004cbafcec9c9b
Reviewed-on: https://chromium-review.googlesource.com/571274Reviewed-by: Jonathan Ross <jonross@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486771}

ui/compositor/compositor.cc

@@ -495,7 +495,13 @@ void Compositor::DidFailToInitializeLayerTreeFrameSink() {
   // The LayerTreeFrameSink should already be bound/initialized before being
   // given to
   // the Compositor.
-  NOTREACHED();
+
+  // TODO(jonross): reenable this once crbug.com/743028 figures out why this is
+  // being reached. Currently one third of all test executions run into this
+  // crbug.com/742966
+  // NOTREACHED();
+  LOG(ERROR) << "Compositor::DidFailToInitializeLayerTreeFrameSink called, "
+             << "when it should be NOTREACHED.";
 }
 
 void Compositor::DidCommit() {