[Import] Add a test file for testing Firefox import code.

The test file is too large to land via the CQ, so landing it manually.
This is in support of [ https://codereview.chromium.org/2296633002 ].

BUG=638977
R=kszatan@opera.com
TBR=kszatan@opera.com

Review URL: https://codereview.chromium.org/2537143006 .

Cr-Commit-Position: refs/heads/master@{#435492}
1 file changed