Use ninja from depot_tools

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "vendor/python-patch"]
 	path = vendor/python-patch
 	url = https://github.com/svn2github/python-patch
+[submodule "vendor/depot_tools"]
+	path = vendor/depot_tools
+	url = https://chromium.googlesource.com/chromium/tools/depot_tools.git

vendor/.gitignore

@@ -1 +0,0 @@
-/depot_tools/

vendor/depot_tools

@@ -0,0 +1 @@
+Subproject commit e3a3fd45aa7f6c247d9e9ab0900164004294fc8d