The new modes process the input data in independent blocks,
using backward references only from within an input block.
The new modes can be used by specifying quality 0 or quality 1,
the old quality 1 and quality 2 modes are renamed quality 2 and
quality 3, respectively, and the old quality 3 mode is removed.
This is used for quality 11, for qualities <= 9 we already
have a simpler hash table.
The static data size is 252 kB, and this removes the
need to initialize a huge hash map at startup, which was
the reason why transforms had to be disabled by default.
In comparison, the static dictionary itself is 120 kB.
This supports every transform, except the kOmitFirstN.
Add a version of the brotli encoder that compresses
each meta-block independently, only using the
original input data from previous meta-blocks
and nothing from the compressor state.
This is a proof-of-concept to show that the
current format is flexible enough to support
parallel multi-threaded compression.
The new mode can be used by setting the greedy_block_split
field of BrotliParams to true.
This commit moves all the meta-block processing code
into its own library and moves the meta-block encoding
code to brotli_bit_stream.cc from encode.cc
