Instead of hard-coding the stock data in the Dart file, this CL moves the data
to a JSON file and loads that file over the network. This change improves load
time for the Stocks app from 3 seconds to 2 seconds.

Also, this CL removes shake-to-reload from the Stocks app because that also
slows down load time (due to the two module systems fighting each other).

R=rafaelw@chromium.org, ojan@chromium.org

Review URL: https://codereview.chromium.org/1021723005