The file snapshot_blob_host.bin was supposed to be generated when building the host toolset. However, the file snapshot_blob.bin was being generated instead, under every set of conditions.

Because of this, every time we build the host toolset, snapshot_blob_host.bin is not found. This causes the target (v8_external_snapshot) that generates such file to be run. This target generates snapshot_blob.bin instead of snapshot_blob_host.bin. This in turn causes all the targets that depend on snapshot_blob.bin to run again.

After this, we still don't have snapshot_blob_host.bin. So the next time we build, the whole process described above happens again.

BUG=421063

Review URL: https://codereview.chromium.org/741223002

Cr-Commit-Position: refs/heads/master@{#25480}
Ensure external snapshot is only set once.

BUG=421063

Review URL: https://codereview.chromium.org/746263002

Cr-Commit-Position: refs/heads/master@{#25481}