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Add the two AppData files, one for Chromium and one for Chrome. The Chrome one
will be filled with the information from the common/google-chrome/google-chrome.info
file and should reflect the current channel (stable, beta, devel). On the other
side the Chromium one should be a general one and it will be reused by
distributions that are packaging the Chromium themselves.

For AppData specification please see:
https://people.freedesktop.org/~hughsient/appdata/

BUG=654190

Review-Url: https://codereview.chromium.org/2424093003
Cr-Original-Commit-Position: refs/heads/master@{#455457}
Committed: https://chromium.googlesource.com/chromium/src/+/d6807b9a7da70dae9191b93d4ec6157187515078
Review-Url: https://codereview.chromium.org/2424093003
Cr-Commit-Position: refs/heads/master@{#455731}