Add candidatewindow* events related IPCs

Add candidatewindow* events related IPCs

These IPCs correspond to Javascript IME API events
(oncandidatewindow*) defined in
https://dvcs.w3.org/hg/ime-api/raw-file/8c061ee19f99/Overview.html#inputmethodcontext-interface

They will fire when IME candidate window changes its appearance.

The Blink side of the change is already checked in:
https://src.chromium.org/viewvc/blink?revision=161139&view=revision

This is the Chromium part of sending IPCs to renderer and
a test for both Chromium and Blink code path, which is not
covered by blink r161139.

The whole change FYI is worked on at
https://codereview.chromium.org/80583002/
and other CLs (to generate actual events from IMEs etc.)
will follow.

BUG=238585
TEST=content_browsertests --gtest_filter="RenderViewImplTest.SendCandidateWindowEvents"

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=238282

[kochi, 2013-11-27 01:38:38]

cevans@chromium.org: Please review changes in 
view_messages.h

jamesr@chromium.org: Please review changes in 
content/renderer/*

sky@chromium.org: Please review changes in 
content/browser/*

ben@chromium.org: Please review changes in 
*_aura*

haraken: CC FYI, adding a test for Blink code path that
you reviewed.

[jamesr, 2013-11-27 01:43:59]

What do these messages mean?

[kochi, 2013-11-27 01:52:00]

On 2013/11/27 01:43:59, jamesr wrote:
> What do these messages mean?

Sorry for the terse description.  I updated the CL description to give more
context.

[kochi, 2013-11-28 11:49:26]

+jln, as cevans is on vacation - could you review view_messages.h?

I assume most other reviewers are on vacation as well,
so I don't expect this to be reviewed ASAP :)

Enjoy your vacation!

[kochi, 2013-12-02 08:42:55]

On 2013/11/28 11:49:26, Takayoshi Kochi wrote:
> +jln, as cevans is on vacation - could you review view_messages.h?
> 
> I assume most other reviewers are on vacation as well,
> so I don't expect this to be reviewed ASAP :)
> 
> Enjoy your vacation!

Pinging everyone - thanks for your time for reviewing this.

[Ben Goodger (Google), 2013-12-02 18:57:50]

rwhva lgtm

[sky, 2013-12-02 22:05:34]

content/browser LGTM

[jln (very slow on Chromium), 2013-12-02 22:09:57]

content/common/view_messages.h lgtm

[jamesr, 2013-12-02 22:18:39]

content/renderer lgtm

[commit-bot: I haz the power, 2013-12-03 00:28:16]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kochi@chromium.org/84963003/90001

[commit-bot: I haz the power, 2013-12-03 03:16:18]

Change committed as 238282