message: Do not assume order on std::unordered_map
  This fixes TF-TRT unit test TRTEngineOpTestBase.DynamicShapes
diff: @@ -135,7 +135,7 @@ TEST_F(TRTEngineOpTestBase, DynamicShapes) {
  // It should contain only one engine.
  auto cache = &cache_resource->cache_;
  EXPECT_EQ(1, cache->size());
  - EXPECT_THAT(cache->begin()->first, ElementsAre(TensorShape({2, 2})));
  + EXPECT_EQ(1, cache->count({TensorShape({2, 2})}));
  // Execute the op with batch size 1. It should reuse existing engine to
  // execute.
  @@ -143,15 +143,15 @@ TEST_F(TRTEngineOpTestBase, DynamicShapes) {
  TRTEngineOpTestBase::AddSimpleInput<float>(TensorShape({1, 2}));
  TF_ASSERT_OK(OpsTestBase::RunOpKernel());
  EXPECT_EQ(1, cache->size());
  - EXPECT_THAT(cache->begin()->first, ElementsAre(TensorShape({2, 2})));
  + EXPECT_EQ(1, cache->count({TensorShape({2, 2})}));
  // Execute the op with a larger batch size.
  ResetInputs();
  TRTEngineOpTestBase::AddSimpleInput<float>(TensorShape({3, 2}));
  TF_ASSERT_OK(OpsTestBase::RunOpKernel());
  EXPECT_EQ(2, cache->size());
  - EXPECT_THAT(cache->begin()->first, ElementsAre(TensorShape({3, 2})));
  - EXPECT_THAT((++cache->begin())->first, ElementsAre(TensorShape({2, 2})));
  + EXPECT_EQ(1, cache->count({TensorShape({2, 2})}));
  + EXPECT_EQ(1, cache->count({TensorShape({3, 2})}));
  // Execute the op with an input that has different non-batch dimension.
  ResetInputs();
  @@ -163,10 +163,9 @@ TEST_F(TRTEngineOpTestBase, DynamicShapes) {
  TRTEngineOpTestBase::AddSimpleInput<float>(TensorShape({1, 10}));
  TF_ASSERT_OK(OpsTestBase::RunOpKernel());
  EXPECT_EQ(3, cache->size()); // Should only create 3 engines in total.
  - auto iter = cache->begin();
  - EXPECT_THAT(iter->first, ElementsAre(TensorShape({10, 10})));
  - EXPECT_THAT((++iter)->first, ElementsAre(TensorShape({3, 2})));
  - EXPECT_THAT((++iter)->first, ElementsAre(TensorShape({2, 2})));
  + EXPECT_EQ(1, cache->count({TensorShape({2, 2})}));
  + EXPECT_EQ(1, cache->count({TensorShape({3, 2})}));
  + EXPECT_EQ(1, cache->count({TensorShape({10, 10})}));
  }
  template <typename T>
  