Support backup request policy #1449

Job	Run time
clang-compile-with-bazel	10m 18s
clang-compile-with-bazel	10m 18s
clang-compile-with-cmake	2m 55s
clang-compile-with-cmake	2m 55s
clang-compile-with-bazel-all-options	10m 29s
clang-compile-with-bazel-all-options	10m 29s
clang-compile-with-boringssl	11m 43s
clang-compile-with-boringssl	11m 43s
clang-compile-with-cmake-all-options	5m 12s
clang-compile-with-cmake-all-options	5m 12s
clang-compile-with-make	2m 45s
clang-compile-with-make	2m 45s
clang-compile-with-make-all-options	4m 44s
clang-compile-with-make-all-options	4m 44s
clang-unittest	6h 0m 13s
clang-unittest	15m 5s
gcc-compile-with-bazel	11m 7s
gcc-compile-with-bazel	11m 7s
gcc-compile-with-bazel-all-options	11m 39s
gcc-compile-with-bazel-all-options	11m 39s
gcc-compile-with-boringssl	12m 50s
gcc-compile-with-boringssl	12m 50s
gcc-compile-with-cmake	3m 15s
gcc-compile-with-cmake	3m 15s
gcc-compile-with-cmake-all-options	5m 38s
gcc-compile-with-cmake-all-options	5m 38s
gcc-compile-with-make	2m 48s
gcc-compile-with-make	2m 48s
gcc-compile-with-make-all-options	5m 12s
gcc-compile-with-make-all-options	5m 12s
	9h 36m 28s

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