Only call finishLoad() if session actually loaded.

BUG=507736
TEST=modified EME browser tests pass (coming in https://codereview.chromium.org/1224053003/)

Review URL: https://codereview.chromium.org/1219753005

git-svn-id: svn://svn.chromium.org/blink/trunk@198532 bbb929c8-8fbe-4397-9dbb-9b2b20218538
1 file changed