Re-apply remoting webapp html in gn

[Chromoting] Enable remoting webapp main.html GN build.

This is a re-land of crrev.com/1082083005

The previous remoting webapp GN build files were not enabled and at
least 6 months out of date. This cl fixes the problem by bringing
the build rules up to date and enables the webapp build.

It also starts to move all the remoting-specific build rules into
the remoting dir rather than having them in the main build.gn file.

BUG=

Committed: https://crrev.com/3eddb5b20af3eb8ae4393ad64fccfd4d69127679
Cr-Commit-Position: refs/heads/master@{#325733}

[garykac, 2015-04-17 18:52:07]

garykac@chromium.org changed reviewers:
+ dpranke@chromium.org

[garykac, 2015-04-17 18:52:07]

This fixes the host build on mac/win (by disabling it).

Manually lauched the Mac/Win GN bots to verify. The failure on the Win GN trybot
is unrelated (bot looks hosed).

[garykac, 2015-04-17 21:06:57]

On 2015/04/17 18:52:07, garykac wrote:
> This fixes the host build on mac/win (by disabling it).
> 
> Manually lauched the Mac/Win GN bots to verify. The failure on the Win GN
trybot
> is unrelated (bot looks hosed).

The Win8 GN trybot failures are due to
https://codereview.chromium.org/1092053002/, which might be reverted soon (the
people involved are in Europe).

[Dirk Pranke, 2015-04-17 21:29:45]

lgtm

[garykac, 2015-04-17 22:13:25]

The CQ bit was checked by garykac@chromium.org

[commit-bot: I haz the power, 2015-04-17 22:14:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1096783002/60001

[commit-bot: I haz the power, 2015-04-17 23:16:46]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-04-17 23:18:08]

Patchset 4 (id:??) landed as
https://crrev.com/3eddb5b20af3eb8ae4393ad64fccfd4d69127679
Cr-Commit-Position: refs/heads/master@{#325733}