Add gn to DEPS file

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 9967e890dc616798f3ca6655b8c4a9b6a26ec49d..2513fc6f0b47a13cf0c7f79096773605cbdebafe 100644
--- a/DEPS
+++ b/DEPS
@@ -69,6 +69,40 @@ hooks = [
     'pattern': '.',
     'action': ['python', 'pdfium/build/gyp_pdfium'],
   },
+  # Pull GN binaries. This needs to be before running GYP below.
+  {
+    'name': 'gn_win',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=win32',
+                '--no_auth',
+                '--bucket', 'chromium-gn',
+                '-s', 'pdfium/buildtools/win/gn.exe.sha1',
+    ],
+  },
+  {
+    'name': 'gn_mac',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=darwin',
+                '--no_auth',
+                '--bucket', 'chromium-gn',
+                '-s', 'pdfium/buildtools/mac/gn.sha1',
+    ],
+  },
+  {
+    'name': 'gn_linux64',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=linux*',
+                '--no_auth',
+                '--bucket', 'chromium-gn',
+                '-s', 'pdfium/buildtools/linux64/gn.sha1',
+    ],
+  },
   # Pull clang-format binaries using checked-in hashes.
   {
     'name': 'clang_format_win',