8a0cc94b1a
As of the migration to Dart 2, it has been necessary to compile Dart to kernel prior to execution. The embedder currently requires that the resulting kernel file be named `kernel_blob.bin` and be located at the root of the assets directory passed to the embedder API. This patch updates the test_fixtures build rule to perform a kernel compile using frontend_server, outputting `kernel_blob.bin` to `fixtures/test_target_name` directory, and updates the embedder unittests to specify the kernel file rather than the Dart source file. Since the kernel compiler requires a `main()` function to be defined, it also updates `simple_main.dart` from runtime_unittests to define `main()` rather than `simple_main()`. This also updates all existing sub-targets to be testonly. This relands commit 4e4fb4608da95d198b0e796478462285ab974a3c, which was reverted in commit 566db0ecb8f293bb9f7ff1fc39076b08336e0148. Rather than running as prebuilt_dart_action, we use dart_action to ensure the frontend snapshot it compatible with the VM on which it's executed.
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