Fix dump_dependency_json generator for iOS

Fix dump_dependency_json generator for iOS

The script tools/gyp-explain.py uses the output of the gyp generator
"dump_dependency_json" so flip the condition in the gyp files to test
if the generator is "xcode" instead of "ninja" (so that the generator
dumping the JSON dependencies see the same dependency as the "ninja"
generator).

BUG=None

Committed: https://crrev.com/51bfded6d6c7ef1ec7e0b7ee939ae83f7358b2a9
Cr-Commit-Position: refs/heads/master@{#318056}

[sdefresne, 2015-02-25 14:45:49]

sdefresne@chromium.org changed reviewers:
+ mark@chromium.org

[sdefresne, 2015-02-25 14:45:50]

Please take a look.

Without this patch, running build/gyp_chromium with
GYP_GENERATORS=dump_dependency_json and GYP_DEFINES=OS=ios fails downstream.

[sdefresne, 2015-02-25 14:57:07]

sdefresne@chromium.org changed reviewers:
+ justincohen@chromium.org

[sdefresne, 2015-02-25 14:57:07]

+justincohen for first review

[justincohen, 2015-02-25 14:57:55]

lgtm

[Mark Mentovai, 2015-02-25 15:27:29]

LGTM

[sdefresne, 2015-02-25 15:29:45]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-02-25 15:31:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/957673005/1

[commit-bot: I haz the power, 2015-02-25 16:19:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-25 16:20:01]

Patchset 1 (id:??) landed as
https://crrev.com/51bfded6d6c7ef1ec7e0b7ee939ae83f7358b2a9
Cr-Commit-Position: refs/heads/master@{#318056}