Use iframe for Chromium perf tests to remove --disable-web-security

[hiroshige-g]

Previously: (a) util_performance_test.js in Blink runs performance tests using (b) pywebsocket's scripts, but this required --disable-web-security for cross-origin workers because (a) and (b) have different origins.

We change this so that: (a) util_performance_test.js creates (c) <iframe> with src=pywebsocket's example/*_iframe.html that runs the performance tests on the iframe using (b) pywebsocket's scripts. Because (b) and (c) have the same origin (but (a) has a different origin), Tests are run in the same-origin while we have an cross-origin iframe.

This CL adds pywebsocket-side iframe HTML/JavaScript files for (b) and (c).

[1] pywebsocket-side: This CL. [2] Chromium-side: https://codereview.chromium.org/1521943002/

BUG=https://code.google.com/p/chromium/issues/detail?id=567533

[hiroshige-g]

tyoshino, could you take a look? Not urgent, but targeting M-49.

[tyoshino]

Could you please fix the OP? It contains HTML tags and entity references. Copied from https://codereview.chromium.org/1521943002 or somewhere?

[hiroshige-g]

Fixed. (it was generated from the commit message and was corrupt because it was interpreted as markdown. Fixed by adding a markdown annotation)

[tyoshino]

lgtm 4f10526e90c3fe94ee2680ebee41928a8a8ae15f