Reland: Mojo: add javascript bindings for request/response

Reland: Mojo: add javascript bindings for request/response

If a mojom interface method specifies response parameters, then we'll generate javascript bindings that provide an additional callback parameter used to pass the response parameters. This mirrors the C++ implementation.

A future improvement will likely be to use promises instead, especially now that they are enabled on trunk.

As part of this CL, connector.js was also made consistent with connector.cc. It starts reading the message pipe immediately, handles write failures in a similar fashion, etc.

The Connection type from connector.js is factored out into a separate file as it now holds a Router object. router.js mirrors router.cc. The Connection type is really the mirror of the C++ RemotePtr<S> type.

Some basic request/response tests were added to connection_unittests.js. We'll probably want more testing.

R=abarth@chromium.org
TBR=mpcomplete@chromium.org

Originally reviewed at https://codereview.chromium.org/207503004/

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=260081

[darin (slow to review), 2014-03-28 06:14:45]

https://codereview.chromium.org/216443002/diff/40001/content/browser/webui/we...
File content/browser/webui/web_ui_mojo_browsertest.cc (right):

https://codereview.chromium.org/216443002/diff/40001/content/browser/webui/we...
content/browser/webui/web_ui_mojo_browsertest.cc:170:
IN_PROC_BROWSER_TEST_F(WebUIMojoTest, DISABLED_EndToEnd) {
This test will be re-enabled on all platforms in
https://codereview.chromium.org/215743002/

[darin (slow to review), 2014-03-28 06:56:28]

Committed patchset #3 manually as r260081 (presubmit successful).