Download and use the goma client from cipd (#41488)

In https://github.com/flutter/flutter/issues/125361 we discovered that a
new version of clang can require updating goma in order for goma to work
properly. This PR adds a dependency on CIPD goma to the DEPS file so
that we can update it for use in local builds when needed. Since CI does
its own management of the goma client and the compiler proxy, and since
goma can only be used by Googlers, the DEPS file download is guarded
behind the `use_cipd_goma` gclient var. To use it one would update the
engine `.gclient` file to be something like:
```
~/flutter/engine/src $ cat ../.gclient
solutions = [
  {
    "managed": False,
    "name": "src/flutter",
    "url": "[email protected]:zanderso/engine.git",
    "custom_deps": {},
    "custom_vars": {
      "use_cipd_goma": True,
    },
    "deps_file": "DEPS",
    "safesync_url": "",
  },
]
```

I'll update the wiki with these instructions after this PR lands.
2 files changed
tree: ca6b7d2b3044ffd97a135982c90e6c5b8de595af
  1. .github/
  2. assets/
  3. benchmarking/
  4. build/
  5. ci/
  6. common/
  7. display_list/
  8. docs/
  9. examples/
  10. flow/
  11. flutter_frontend_server/
  12. flutter_vma/
  13. fml/
  14. impeller/
  15. lib/
  16. runtime/
  17. shell/
  18. sky/
  19. testing/
  20. third_party/
  21. tools/
  22. vulkan/
  23. wasm/
  24. web_sdk/
  25. .ci.yaml
  26. .clang-format
  27. .clang-tidy
  28. .gitattributes
  29. .gitignore
  30. .pylintrc
  31. .style.yapf
  32. analysis_options.yaml
  33. AUTHORS
  34. BUILD.gn
  35. CODEOWNERS
  36. CONTRIBUTING.md
  37. DEPS
  38. Doxyfile
  39. LICENSE
  40. README.md
README.md

Flutter Engine

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