Fix an off-by-one error in checking # of action context menu items in

Fix an off-by-one error in checking # of action context menu items in
  chrome.contextMenus.

We should not increment |num_items| if we're not adding the item to the
  menu model. We have a test for this already:
  ExtensionContextMenuModelTest::ExtensionItemTest, since that is looking
  at |num_items| to verify
  (by ExtensionContextMenuModelTest::CountExtensionItems()).

BUG=463467
Test=Add 6 browser_action items from an extension that has "contextMenus" permission:
for (var i = 0; i < chrome.contextMenus.ACTION_MENU_TOP_LEVEL_LIMIT; i++) {
  (function(idx) {
    chrome.contextMenus.create({ contexts: [ "browser_action" ], title: "entry " + idx }, function() {
      console.debug("created " + idx, chrome.runtime.lastError);
    })
  })(i);
}
Expect all 6 (ACTION_MENU_TOP_LEVEL_LIMIT) items to show up when you right
click the extension icon in browser toolbar.

Committed: https://crrev.com/413226da7a9a50853005b83a440c8026f823163a
Cr-Commit-Position: refs/heads/master@{#329948}

[lazyboy, 2015-05-08 16:13:20]

lazyboy@chromium.org changed reviewers:
+ rdevlin.cronin@chromium.org

[Devlin, 2015-05-08 16:34:04]

Can we modify the unittest to verify this particular case, so we don't regress?

[lazyboy, 2015-05-08 22:53:39]

On 2015/05/08 16:34:04, Devlin wrote:
> Can we modify the unittest to verify this particular case, so we don't
regress?

OK, I've modified the test to look at item labels and verify
that correct number of items are present in MenuModel.
It's not the prettiest way to do it, but it does the job and
catches the regression (the test will fail w/o the change).

Patch Set #2

https://chromiumcodereview.appspot.com/1137733002/diff/20001/chrome/browser/e...
File chrome/browser/extensions/extension_context_menu_model_unittest.cc (right):

https://chromiumcodereview.appspot.com/1137733002/diff/20001/chrome/browser/e...
chrome/browser/extensions/extension_context_menu_model_unittest.cc:122:
model->Clear();
This used to be a bug in the test.

[Devlin, 2015-05-14 20:59:31]

lgtm

[lazyboy, 2015-05-14 21:16:25]

The CQ bit was checked by lazyboy@chromium.org

[commit-bot: I haz the power, 2015-05-14 21:19:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1137733002/20001

[commit-bot: I haz the power, 2015-05-14 22:18:28]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-14 22:20:09]

Patchset 2 (id:??) landed as
https://crrev.com/413226da7a9a50853005b83a440c8026f823163a
Cr-Commit-Position: refs/heads/master@{#329948}