Disable LayerTreeHostScrollbarsPixelTest.HugeTransformScale on TSan

Disable the test on TSan builders due to frequent timeouts.

TBR=danakj@chromium.org

Bug: 848994
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I6ddeb111e2ee2432b958b6981ab4099e8e1c89b3
Reviewed-on: https://chromium-review.googlesource.com/1084830
Commit-Queue: Dominic Battré <battre@chromium.org>
Reviewed-by: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564052}

cc/trees/layer_tree_host_pixeltest_scrollbars.cc

@@ -137,7 +137,13 @@ TEST_F(LayerTreeHostScrollbarsPixelTest, TransformScale) {
                base::FilePath(FILE_PATH_LITERAL("spiral_double_scale.png")));
 }
 
-TEST_F(LayerTreeHostScrollbarsPixelTest, HugeTransformScale) {
+// Disabled on TSan due to frequent timeouts. crbug.com/848994
+#if defined(THREAD_SANITIZER)
+#define MAYBE_HugeTransformScale DISABLED_HugeTransformScale
+#else
+#define MAYBE_HugeTransformScale HugeTransformScale
+#endif
+TEST_F(LayerTreeHostScrollbarsPixelTest, MAYBE_HugeTransformScale) {
   scoped_refptr<SolidColorLayer> background =
       CreateSolidColorLayer(gfx::Rect(400, 400), SK_ColorWHITE);