[HHH] update ENGINE_PATH

After https://dart-review.googlesource.com/c/recipes/+/175080 the
ENGINE_PATH should have an extra folder.

ENGINE_PATH: /b/s/w/ir/cache/builder is failing.
ENGINE_PATH: /b/s/w/ir/cache/builder/engine should work.

The following works locally, indicating ENGINE_PATH should point to the
engine folder:
ENGINE_PATH=~/flt/engine WEB_UI_DIR=~/flt/engine/src/flutter/lib/web_ui/ src/flutter/lib/web_ui/dev/web_engine_analysis.sh

Change-Id: I551def9d65932287430e3ce9c805dfdb8f43d2d2
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/176260
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
4 files changed