Store target app name in Web Share prefs, and remove external logic.

UpdateShareTargetInPrefs now stores the name field of the supplied
target's manifest in the Web Share target prefs. For the given share
target, adds the name to the dictionary associated with the target.

UpdateShareTargetInPrefs also handles the logic about web apps with
manifests that don't have the share_target field, entirely internally.

BUG=668389

Review-Url: https://codereview.chromium.org/2679523002
Cr-Commit-Position: refs/heads/master@{#448568}
4 files changed