Roll src/third_party/leveldatabase/src/ 186839815..f7b0e1d90 (3 commits)

https://chromium.googlesource.com/external/leveldb.git/+log/18683981505d..f7b0e1d901da

$ git log 186839815..f7b0e1d90 --date=short --no-merges --format='%ad %ae %s'
2018-08-14 costan Expose WriteBatch::Append().
2018-06-04 costan Clean up Iterator.
2018-05-21 cmumford Corrected typo in docs: "cache" to "block_cache".

Created with:
  roll-dep src/third_party/leveldatabase/src

Bug: 862456
Change-Id: I8c618f5311d0f13fc59449be3c228b4aa63403ef
Reviewed-on: https://chromium-review.googlesource.com/1174981
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583510}

DEPS

@@ -777,7 +777,7 @@ deps = {
   },
 
   'src/third_party/leveldatabase/src':
-    Var('chromium_git') + '/external/leveldb.git' + '@' + '18683981505dc374ce29211c80a9552f8f2f4571',
+    Var('chromium_git') + '/external/leveldb.git' + '@' + 'f7b0e1d901da26ac5ce6ad7f0a9806ce1440197e',
 
   'src/third_party/libFuzzer/src':
     Var('chromium_git') + '/chromium/llvm-project/compiler-rt/lib/fuzzer.git' + '@' +  Var('libfuzzer_revision'),