Install ninja using DEPS

We are going to install ninja CIPD to third_party.
https://crrev.com/c/4005475

This CL adds `.gitignore` and `README.nacl` for the change.

Bug: chromium:1340825
Change-Id: Ibf6610432d48de849a9eb886ba25fbfb29dd63d0
Reviewed-on: https://chromium-review.googlesource.com/c/native_client/src/third_party/+/4005416
Reviewed-by: Derek Schuff <dschuff@chromium.org>
Auto-Submit: Junji Watanabe <jwata@google.com>
diff --git a/.gitignore b/.gitignore
index c947801..6b8b06c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,11 +1,12 @@
 *.pyc
 
 # DEPS
-/ragel
-/lss
 /NSIS
-/valgrind
 /lcov
+/lss
+/ninja/ninja*
+/ragel
+/valgrind
 
 # gclient hooks
 /llvm-build
diff --git a/ninja/README.nacl b/ninja/README.nacl
new file mode 100644
index 0000000..0691448
--- /dev/null
+++ b/ninja/README.nacl
@@ -0,0 +1,17 @@
+Name: ninja
+Short Name: ninja
+URL: https://github.com/ninja-build/ninja
+Revision: See the CIPD version in src/native_client/DEPS
+License: Apache License 2.0
+License File: https://github.com/ninja-build/ninja/blob/master/COPYING
+Security Critical: no
+
+Description:
+Ninja is a small build system with a focus on speed, and is used to build
+this project.
+
+The CIPD packages are built using the 3pp pipeline.
+https://chromium.googlesource.com/infra/infra/+/refs/heads/main/3pp/ninja/
+
+Local Modifications:
+None