merge(3p/absl): subtree merge of Abseil up to e19260f

... notably, this includes Abseil's own StatusOr type, which
conflicted with our implementation (that was taken from TensorFlow).

Change-Id: Ie7d6764b64055caaeb8dc7b6b9d066291e6b538f

third_party/abseil_cpp/ci/cmake_common.sh

@@ -0,0 +1,25 @@
+# Copyright 2020 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# The commit of GoogleTest to be used in the CMake tests in this directory.
+# Keep this in sync with the commit in the WORKSPACE file.
+readonly ABSL_GOOGLETEST_COMMIT="8567b09290fe402cf01923e2131c5635b8ed851b"
+
+# Avoid depending on GitHub by looking for a cached copy of the commit first.
+if [[ -r "${KOKORO_GFILE_DIR:-}/distdir/${ABSL_GOOGLETEST_COMMIT}.zip" ]]; then
+  DOCKER_EXTRA_ARGS="--mount type=bind,source=${KOKORO_GFILE_DIR}/distdir,target=/distdir,readonly ${DOCKER_EXTRA_ARGS:-}"
+  ABSL_GOOGLETEST_DOWNLOAD_URL="file:///distdir/${ABSL_GOOGLETEST_COMMIT}.zip"
+else
+  ABSL_GOOGLETEST_DOWNLOAD_URL="https://github.com/google/googletest/archive/${ABSL_GOOGLETEST_COMMIT}.zip"
+fi