Install CIPD ninja using DEPS

See chromium/src's CL https://crrev.com/c/3869740 for the context.

Bug: chromium:1340825
Change-Id: I7cd5f576b28f10fdbf5aa3a6ccb3a878af46d24e
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/101130
Auto-Submit: Junji Watanabe <jwata@google.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
diff --git a/.gitignore b/.gitignore
index c0df1c2..aeb1e05 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,10 +8,10 @@
 /third_party/android_ndk
 /third_party/catapult
 /third_party/depot_tools
+/third_party/freetype/src
 /third_party/fuchsia-sdk/images
 /third_party/fuchsia-sdk/images-internal
 /third_party/fuchsia-sdk/sdk
-/third_party/freetype/src
 /third_party/googletest/src
 /third_party/icu
 /third_party/instrumented_libraries
@@ -22,6 +22,7 @@
 /third_party/lss
 /third_party/markupsafe
 /third_party/nasm
+/third_party/ninja/ninja*
 /third_party/skia
 /third_party/test_fonts
 /third_party/zlib