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

When iter_ is pointing to current key, we can safely move to the next
key to avoid checking current key, which is of course not necessary.

Benchmark shows that 'readseq' has about 8% performance improvement.

Without patch:

>./db_bench --benchmarks=readseq --num=$((4<<20)) --db=/tmp/db --use_existing_db=1
LevelDB:    version 1.21
Date:       Thu Apr 25 09:37:21 2019
CPU:        32 * Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz
CPUCache:   20480 KB
Keys:       16 bytes each
Values:     100 bytes each (50 bytes after compression)
Entries:    4194304
RawSize:    464.0 MB (estimated)
FileSize:   264.0 MB (estimated)
------------------------------------------------
readseq      :       0.196 micros/op;  565.7 MB/s

With patch:

>./db_bench --benchmarks=readseq --num=$((4<<20)) --db=/tmp/db --use_existing_db=1
LevelDB:    version 1.21
Date:       Thu Apr 25 09:38:20 2019
CPU:        32 * Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz
CPUCache:   20480 KB
Keys:       16 bytes each
Values:     100 bytes each (50 bytes after compression)
Entries:    4194304
RawSize:    464.0 MB (estimated)
FileSize:   264.0 MB (estimated)
------------------------------------------------
readseq      :       0.181 micros/op;  612.3 MB/s

Signed-off-by: Kyle Zhang <kyle@smartx.com>

ssize_t is not standard C++. It is a POSIX extension. Therefore, it does
not belong in generic code.

This change tweaks the logic in DBIter to remove the need for signed
integers, so ssize_t can be replaced with size_t. The impacted method
and private member are renamed to better express their purpose.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=211471606

Fix issues 200, 201

Also,
* Fix link to bigtable paper in docs.
* New sstables will have the file extension .ldb. .sst files will
continue to be recognized.
* When building for iOS, use xcrun to execute the compiler. This may
affect issue 177.

Fix issues 77, 87, 182, 190.

Additionally, fix the bug described in
https://groups.google.com/d/msg/leveldb/yL6h1mAOc20/vLU64RylIdMJ
where a large contiguous keyspace of deleted data was not getting
compacted.

Also fix a bug where options.max_open_files was not getting clamped
properly.

- 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)

- Fix bug in Iterator::Prev where it would return the wrong key.
  Fixes issues 29 and 30.

- Added a tweak to testharness to allow running just some tests.

- Fixing two minor documentation errors based on issues 28 and 25.

- Cleanup; fix namespaces of export-to-C code.
  Also fix one "const char*" vs "char*" mismatch.



git-svn-id: https://leveldb.googlecode.com/svn/trunk@48 62dab493-f737-651d-591e-8d6aee1b9529

* env_chromium.cc should not export symbols.
* Fix MSVC warnings.
* Removed large value support.
* Fix broken reference to documentation file

git-svn-id: https://leveldb.googlecode.com/svn/trunk@24 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@18 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@16 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@15 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@14 62dab493-f737-651d-591e-8d6aee1b9529

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