Disable LayerTreeHostImplTest.OnMemoryPressure on chromecast as well

The test case has generated a test failure on chromecase as well. I guess that
ProcessMetric doesn't work on some platforms well. Once this CL disables it like
other platforms. Then, new CL will try to fix the failure for all platforms.

Bug: 839687
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I34794c3816c3301fd7535bd2d2d2b5c0e70b21ec
Reviewed-on: https://chromium-review.googlesource.com/1084146
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Gyuyoung Kim <gyuyoung.kim@lge.com>
Cr-Commit-Position: refs/heads/master@{#564340}

cc/trees/layer_tree_host_impl_unittest.cc

@@ -11612,12 +11612,12 @@ TEST_F(LayerTreeHostImplTest, OnDrawConstraintSetNeedsRedraw) {
   EXPECT_FALSE(last_on_draw_frame_->has_no_damage);
 }
 
-// TODO(gyuyoung): OnMemoryPressure disabled on ASAN, TSAN, Android, windows
-//                 due to the test failure. Will be handled on
+// TODO(gyuyoung): OnMemoryPressure disabled on ASAN, TSAN, Android, windows,
+//                 chromecast due to the test failure. Will be handled on
 //                 http://crbug.com/839687.
 #if defined(OS_WIN) || defined(OS_ANDROID) || defined(ADDRESS_SANITIZER) || \
     defined(THREAD_SANITIZER) || defined(MEMORY_SANITIZER) ||               \
-    defined(LEAK_SANITIZER)
+    defined(LEAK_SANITIZER) || defined(CHROMECAST_BUILD)
 #define MAYBE_OnMemoryPressure DISABLED_OnMemoryPressure
 #else
 #define MAYBE_OnMemoryPressure OnMemoryPressure