John "codefu" McDole ff983d3598
feat: start using the content aware hash for downloading artifacts (#172552)
reland of https://github.com/flutter/flutter/pull/171927
towards https://github.com/flutter/flutter/issues/171790

Use the content aware hash when downloading engine artifacts. These are
currently produced when changes to DEPs, engine/, or the release file
are changed in a not-seen-before way.

We can eventually remove engine.version being tracked in release
branches as an optimization.

FLUTTER_PREBUILT_ENGINE_VERSION will stay for overriding the
engine.version for testing. Though Cocoon does not need to actually set
it for framework only PRs anymore.

fxies post submit tests for content_hash download:
SHARD=framework_tests SUBSHARD=misc dart --enable-asserts
dev/bots/test.dart
SHARD=tool_host_cross_arch_tests dart --enable-asserts
dev/bots/test.dart

```
  ╔═╡ERROR https://github.com/flutter/flutter/pull/1╞════════════════════════════════════════════════════════════════════
  ║ Expected "Flutter Engine Version: 45b085ab2118f30441ae6e2daab4b8eb3e4a063c", but found "Flutter Engine Version: 407c051ec9".
  ╚═══════════════════════════════════════════════════════════════════════════════
```

```
  Expected: contains '45b085ab2118f30441ae6e2daab4b8eb3e4a063c'
     Which: does not contain '45b085ab2118f30441ae6e2daab4b8eb3e4a063c'
```
2025-07-22 17:35:26 +00:00
..