Mark GpuCrash_InfoForDualHardwareGpus as flaky on Mac

The test only runs on Mac with dual GPUs right now.

Mark it as flaky to unblock CQ until we resolve the real issue
underlying.

BUG=1164647
TEST=bots
R=kbr@chromium.org

Change-Id: I0b9d2469abc6dbfd1c59809ce1c7c5455c860047
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2620088
Auto-Submit: Zhenyao Mo <zmo@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842069}

content/test/gpu/gpu_tests/test_expectations/context_lost_expectations.txt

@@ -137,3 +137,6 @@ crbug.com/1154047 [ fuchsia ] GpuCrash_InfoForHardwareGpu [ Skip ]
 # Flaky hangs on Mac Debug NVIDIA, stalling the test suite for 40 minutes
 crbug.com/1161570 [ mac nvidia debug ] GpuCrash_InfoForHardwareGpu [ Skip ]
 crbug.com/1161570 [ mac nvidia debug ] GpuCrash_InfoForDualHardwareGpus [ Skip ]
+
+# Flaky on dual GPU Mac.
+crbug.com/1164647 [ mac amd ] GpuCrash_InfoForDualHardwareGpus [ RetryOnFailure ]