Use bloom filter in multi bigram map.

Evaluated with previous word "this".
without bloom filter (use only hash_map):
Total 147792.34 (sum of others 147771.57)
with bloom filter:
Total 145900.64 (sum of others 145874.30)
always read binary dictionary:
Total 148603.14 (sum of others 148579.90)

Bug: 8592527
Change-Id: I821dc39454543826adb73b9eeeef6408fad8ae28