Fix inconsistent code format

Summary:
Found some function follows camel style. When naming funciton, we have two styles:

Trivially expose internal data in readonly mode: `all_lower_case()`
Regular function: `CapitalizeFirstLetter()`

I renames these functions.

Test Plan: make -j32

Reviewers: haobo, sdong, dhruba, igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16383