While we are at it:
- Rename some variables to more meaningful names
- Reuse some common consts from a header instead of redefining them.

Cherry-picked from aomedia/master: 863b0499

Change-Id: Ida5de713156dc0126a27f90fdd36d29a398a3c88

- Change struct name to all caps SCAN_ORDER to be locally consistent.
- Rename struct pointers to 'scan_order' instead of hard to read short
  names 'so' and 'sc'.

Cherry-picked from aomedia/master: 30abc082

Change-Id: Ib9f0eefe28fa97d23d642b77d7dc8e5f8613177d

While we are at it:
- Rename some variables to more meaningful names
- Reuse some common consts from a header instead of redefining them.

Cherry-picked from aomedia/master: 09eea219

Change-Id: I61030e773137ae107d3bd43556c0d5bb26f9dbf8

In the header, all we need is number of stat types, not the names for actual
types.

Removing it avoids names like 'Y', 'U', 'V' and 'ALL' being visible
in all files that include the encoder.h header.

Change-Id: I874a73a3cfe6bcb29aedea102077a52addc49af6

- Const correctness
- Refactoring
- Make variables local when possible etc
- Remove -Wcast-qual to allow explicitly casting away const.

Cherry-picked from aomedia/master: c27fcccc
And then a number of more const correctness changes to make sure other
experiments build OK.

Change-Id: I77c18d99d21218fbdc9b186d7ed3792dc401a0a0

Change-Id: Ibc73b4066dcdee45d32355144124762d26a16a28

Change-Id: Ifcc329df240c0771172180933a6180b21fd31abe

This is not used since the commint 00cd5de5,
"Remove skip_recode speed feature".

Change-Id: Ic03da6c0095f6285a3889d5d22e8aaa2e6cbfd79

On average no compression performance changes. Encoding speed is
increased by 10~20% on some test clips in the derf set.

Change-Id: I9856caaa260303f6f6259686671bed7d51012277

Drop some speed features used in speed 2 and above, during the
algorithm development process. This helps simplify the codebase.

Change-Id: I3b2f5560d90b00d2d8fd57c2cb36f6ddd3f228e4

Change-Id: I65c04006f6e6eb13ceb22efc1c39915cb3c82b82

Change-Id: Ic11eae36c9c62a20699197847aa3ef9562d4ad7e

Change-Id: Ie90dd06c387119ccd9c920a328c942477df00bb7

This commit ports the following from aom/master:
4c462788 Add aom_reader_tell() support.
b9c99350 Remove an erroneous declaration.
56c9c3bf Fix ANS build.

Change-Id: I59bd910f58c218c649a1de2a7b5fae0397e13cb1

This computation should match the code in encode_block
to increase the accuracy of the rd optimization.

Change-Id: Ibc9d9ab6d88d0c0f3af62e9cc233216aba48a57e

When built with var_tx and ext_tx, select_tx_size_fix_type is used
to compute the cost for using a particular tx_type.
The code indexes the array inter_tx_type_costs at the wrong location
resulting in a zero cost for signalling tx_type for rect_tx blocks.

Change-Id: Iba38be3a0d822109f778f0600b242dfb40359766

Change-Id: I33899eca44300037816c9f20c965aa8311a1ef52

Change-Id: I35f85bad88c637cea62577c546cdd5ced0e21bd6

Will break ext-intra into 2 experiments: ext-intra and filter-intra.

Change-Id: Ibf66e9b9d9307fd58a703eada9569b74d171434b

To get ready for pulling AV1 to nextgenv2. Refactoring is done to
make the code structures similar, especially for the motion search
part.

Change-Id: I5d7636394408d97de55394d668540f5627827983