GitLab

Now group previous multiple virtual test suites with the same
prefix and args together.

For example, previous configuration
  {
    "prefix": "composite-after-paint",
    "base": "compositing",
    "args": ["--enable-blink-features=CompositeAfterPaint"]
  }
  {
    "prefix": "composite-after-paint",
    "base": "paint",
    "args": ["--enable-blink-features=CompositeAfterPaint"]
  }
now becomes
  {
    "prefix": "composite-after-paint",
    "bases": ["compositing",
              "paint"],
    "args": ["--enable-blink-features=CompositeAfterPaint"]
  }

This shortens VirtualTestSuites by nearly half, avoids accidental
inconsistent args (We should create different virtual test suite
for different args), and allow "pure physical" virtual test suite
which is an alternative of physical test suite.

A "pure physical" virtual test suite has empty "bases", and the
"virtual/<prefix>" test path contains real tests only.

Normal vitual test suites can still contain real tests.

Bug: 1014162
Change-Id: I8d24be0e62b44ec8987aef65cb6f9ff0423b2d2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1873504
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710210}