Allow users to profile a query and see bottleneck of the query

Summary:
Provide a framework to profile a query in detail to figure out latency bottleneck. Currently, in Get(), Put() and iterators, 2-3 simple timing is used. We can easily add more profile counters to the framework later.

Test Plan: Enable this profiling in seveal existing tests.

Reviewers: haobo, dhruba, kailiu, emayanke, vamsi, igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14001

Conflicts:
	table/merger.cc
Add BloomFilter to PlainTableIterator::Seek()

Summary:
This patch adds a simple bloom filter in PlainTableIterator::Seek()

Test Plan: N/A

Reviewers:

CC:

Task ID: #

Blame Rev:
[For Performance Branch] Bloom filter in PlainTableIterator::Seek() - Update 1

Summary:
Address @haobo's comments in D14277

Test Plan: ./indexed_table_db_test

Reviewers: haobo

CC:

Task ID: #

Blame Rev: