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

Windows linking visibility in shared libraries requires that inner classes are
specifically exported as visible, even if the containing class is exported.

PiperOrigin-RevId: 244886019

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=229395810

WriteBatchInternal has a method for efficiently concatenating two
WriteBatches. This commit exposes the method to the public API.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=208724311

This CL switches the public headers to C++11 default and deleted constructors, and adds override to the relevant leveldb::EnvWrapper methods. This should be a good test for C++11 compiler support.

Once this CL settles, the rest of the codebase can be safely modernized to C++11.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=189873212

gcc defaults to exporting all symbols, but other linkers do not. Adding
the LEVELDB_EXPORT macro allows a project to set LEVELDB_SHARED_LIBRARY
when building/linking with leveldb as a shared library.

This is to allow leveldb to be created as a shared library on all
platforms support by Chrome and enables a fix for
https://bugs.chromium.org/p/chromium/issues/detail?id=764810.

This also has the benefit of reducing the shared library size from
418863 to 380367 bytes (64-bit Linux).

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171037148

This can be used to report metrics on LevelDB usage.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=156934930

- Replace raw slice comparison with a call to user comparator.
  Added test for custom comparators.

- Fix end of namespace comments.

- Fixed bug in picking inputs for a level-0 compaction.

  When finding overlapping files, the covered range may expand
  as files are added to the input set.  We now correctly expand
  the range when this happens instead of continuing to use the
  old range.  For example, suppose L0 contains files with the
  following ranges:

      F1: a .. d
      F2:    c .. g
      F3:       f .. j

  and the initial compaction target is F3.  We used to search
  for range f..j which yielded {F2,F3}.  However we now expand
  the range as soon as another file is added.  In this case,
  when F2 is added, we expand the range to c..j and restart the
  search.  That picks up file F1 as well.

  This change fixes a bug related to deleted keys showing up
  incorrectly after a compaction as described in Issue 44.

(Sync with upstream @25072954)

Check the NEWS file for details of what changed.

git-svn-id: https://leveldb.googlecode.com/svn/trunk@28 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@23 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@21 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@20 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@19 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@2 62dab493-f737-651d-591e-8d6aee1b9529