[ios] Remove IDC_BACK and IDC_FORWARD

[ios] Remove IDC_BACK and IDC_FORWARD

- Adds a dispatcher to ToolbarController.

- Adds -goBack and goForward to BrowserCommands.

BUG=738881
TEST=Manually tested forward/back in simulator

[marq (ping after 24h), 2017-07-03 09:24:13]

The CQ bit was checked by marq@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-07-03 09:24:28]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-07-03 09:53:51]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-07-03 09:53:53]

Dry run: Try jobs failed on following builders:
  ios-device-xcode-clang on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device-xcode-...)

[marq (ping after 24h), 2017-07-03 13:28:46]

Description was changed from

==========
[ios] Remove IDC_BACK and IDC_FORWARD

BUG=
==========

to

==========
[ios] Remove IDC_BACK and IDC_FORWARD

BUG=738881
==========

[marq (ping after 24h), 2017-07-04 09:39:05]

Description was changed from

==========
[ios] Remove IDC_BACK and IDC_FORWARD

BUG=738881
==========

to

==========
[ios] Remove IDC_BACK and IDC_FORWARD

- Adds a dispatcher to ToolbarController.

- Adds -goBack and goForward to BrowserCommands.

BUG=738881

TEST=Manually tested forward/back in simulator
==========

[marq (ping after 24h), 2017-07-04 09:48:25]

Rebase, self review.

[marq (ping after 24h), 2017-07-04 13:07:59]

The CQ bit was checked by marq@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-07-04 13:08:12]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-07-04 13:10:21]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-07-04 13:10:23]

Dry run: Try jobs failed on following builders:
  ios-device on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device/builds...)
  ios-simulator-xcode-clang on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator-xco...)
  mac_chromium_compile_dbg_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)