[Sheriff] Disable flaky DroppedFrameCounterMainDrops* tests

TBR=sadrul@chromium.org

Bug: 1115376
Change-Id: I2245dfb061fba74f29e4702c79f537253bfe3d7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2395656Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804731}

cc/metrics/dropped_frame_counter_unittest.cc

@@ -226,7 +226,8 @@ class DroppedFrameCounterMainDropsNoSmoothness
   }
 };
 
-MULTI_THREAD_TEST_F(DroppedFrameCounterMainDropsNoSmoothness);
+// TODO(crbug.com/1115376) Disabled for flakiness.
+// MULTI_THREAD_TEST_F(DroppedFrameCounterMainDropsNoSmoothness);
 
 class DroppedFrameCounterMainDropsSmoothnessTest
     : public DroppedFrameCounterTestBase {
@@ -243,7 +244,8 @@ class DroppedFrameCounterMainDropsSmoothnessTest
   }
 };
 
-MULTI_THREAD_TEST_F(DroppedFrameCounterMainDropsSmoothnessTest);
+// TODO(crbug.com/1115376) Disabled for flakiness.
+// MULTI_THREAD_TEST_F(DroppedFrameCounterMainDropsSmoothnessTest);
 
 }  // namespace
 }  // namespace cc