The previous attempt of having EnvPosix use O_CLOEXEC (close-on-exec()) when opening file descriptors added tests that relied on procfs, which is Linux-specific. These tests failed on macOS. Unfortunately, the test failures were not caught due to a (since fixed) error in our Travis CI configuration.

This CL re-structures the tests to only rely on POSIX features. Since there is no POSIX-compliant way to get a file name/path out of a file descriptor, this CL breaks up the O_CLOEXEC test into multiple tests, where each Env method that creates an FD gets its own test. This is intended to make it easier to find and fix errors in Env implementations.

This CL also fixes the implementation of NewLogger() to use O_CLOEXEC on macOS. The current implementation passes "we" to fopen(), but the macOS standard C library does not implement the "e" flag yet.

PiperOrigin-RevId: 247088953

Two minor corrections to correct the 900f7d37eb commit
to conform to the Google C++ style guide.

PiperOrigin-RevId: 246907647

1. Correct the class/struct declaration order to be IAW
   the Google C++ style guide[1].
2. For non-copyable classes, switched from non-implemented
   private methods to explicitly deleted[2] methods.
3. Minor const and member initialization fixes.

[1] https://google.github.io/styleguide/cppguide.html#Declaration_Order
[2] http://eel.is/c++draft/dcl.fct.def.delete

PiperOrigin-RevId: 246521844

Use clang-format to correct formatting to be in agreement with the [Google C++ Style Guide](https://google.github.io/styleguide/cppguide.html). Doing this simplifies the process of accepting changes. Also fixed a few warnings flagged by clang-tidy.

PiperOrigin-RevId: 246350737

This prevents file descriptors from leaking to child processes.

When compiled for older (pre-2.6.23) kernels which lack support for
O_CLOEXEC there is no change in behavior.  With newer kernels, child
processes will no longer inherit leveldb's file handles, which
reduces the changes of accidentally corrupting the database.

Fixes https://github.com/google/leveldb/issues/623

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=192365747

env_test.cc defines EnvPosixTest which tests the Env implementation returned by Env::Default(). The naming is a bit unfortunate, as the tests in env_test.cc are written against the Env contract, and therefore are applicable to any Env implementation. An instance of the confusion caused by the naming is [] which added a dependency from env_test.cc to EnvPosixTestHelper, which is closely coupled to EnvPosix.

This change disentangles EnvPosix-specific test code into a env_posix_test.cc file. The code there uses EnvPosixTestHelper and specifically targets the EnvPosix implementation. env_test.cc now implements EnvTest, and contains tests that are also applicable to other ports, which may define their own Env implementation.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148914642