*** PLEASE DO NOT REVERT ***
Please file a bug blocking crbug.com/771643 cc wangxianzhu@chromium.org
chrishtr@chromium.org and vmpstr@chromium.org if you encounter any problem
after this CL.

After this change:
- All blink unit tests and layout tests will run with SPv175 enabled
  by default;
- We no longer have virtual/spv175 and flag-specific/enable-slimming-paint-v175;
- We'll still have non-spv175 test coverage:
  - Many paint related tests still run with multiple configurations;
  - Several sub-directories of layout tests will be run as
    virtual/disable-spv175;
  - We may periodically try all tests with spv175 disabled on bots.

Steps to generate this CL (similar to crrev.com/c/893624
which was for RootLayerScrolling, with some differences because we didn't
have baselines for SPv175 for platforms other than linux before):

1. Merge FlagExpectations/enable-slimming-paint-v175 into TestExpectations;

2. Remove original virtual/spv175/ prefix for SPv175-specific failures in
   TestExpectations;

3. Change VirtualTestSuites to change original spv175 virtual suites to
   disable-spv175 suites using --disable-blink-features=SlimmingPaintV175;

4. Change original virtual/spv175/ failure expectations that were not
   SPv175 to virtual/disable-spv175/, in TestExpectations, SlowTests and
   other expectation files;

5. For each baseline files under flag-specific/enable-slimming-paint-v175,
   search the existing non-spv175 baseline in the order of platform/linux,
   platform/win and base dir, and overwrite the first found existing
   baseline with the spv175 one.

6. For each baseline files under virtual/spv175, search the existing
   non-spv175 baseline in the order of platform/linux, platform/win
   and base dir, and swap the two baselines;

7. Rename virtual/spv175 to virtual/disable-spv175, and update the
   README.txt files.

8. Upload the CL, and run webkit-patch rebaseline-cl.

9. When the try jobs finish, examine the try results, and run
   webkit-patch rebaseline-cl again to rebaseline the tests that failed
   on windows and mac (for which we didn't have spv175 baselines).

Bug: 771643
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_layout_ng;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Iedcdcc881e7ef43bc573a7f4b51ebe2bfbbbc411
Reviewed-on: https://chromium-review.googlesource.com/917226Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537398}