Add in basic BUILD.gn and additional DEPS

This is a minimal config that gets us building the tint binary from samples/

BUG=tint:2

Change-Id: Ifafa903e99a34f1c47177eb954df69ecbe70cb36
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/19106
Reviewed-by: dan sinclair <dsinclair@google.com>

DEPS

@@ -4,6 +4,10 @@ vars = {
   'chromium_git':  'https://chromium.googlesource.com',
   'github': '/external/github.com',
 
+  'binutils_revision': '01aa7745b0bab64ae22600f09fd6483c60f22ebf',
+  'build_revision': 'f3d0ca5f46b7b190dbbdc6be508ca11dd5c54302',
+  'buildtools_revision': '74cfb57006f83cfe050817526db359d5c8a11628',
+  'clang_revision': '3605577b67603ec5776afcfada9e0ff4ea05cf0e',
   'cpplint_revision': '305ac8725a166ed42e3f5dd3f80d6de2cf840ef1',
   'googletest_revision': '482ac6ee63429af2aa9c44f4e6427873fb68fb1f',
   'spirv_headers_revision': 'f8bf11a0253a32375c32cad92c841237b96696c0',
@@ -22,4 +26,120 @@ deps = {
 
   'third_party/spirv-tools': Var('chromium_git') + Var('github') +
       '/KhronosGroup//SPIRV-Tools.git@' + Var('spirv_tools_revision'),
+
+  # Dependencies required to use GN/Clang in standalone
+  'build': Var('chromium_git') + '/chromium/src/build@' +
+      Var('build_revision'),
+
+  'buildtools': Var('chromium_git') + '/chromium/src/buildtools@' +
+      Var('buildtools_revision'),
+
+  'tools/clang': Var('chromium_git') + '/chromium/src/tools/clang@' +
+      Var('clang_revision'),
+
+  'third_party/binutils': Var('chromium_git') +
+      '/chromium/src/third_party/binutils@' + Var('binutils_revision'),
 }
+
+hooks = [
+  # Pull clang-format binaries using checked-in hashes.
+  {
+    'name': 'clang_format_win',
+    'pattern': '.',
+    'condition': 'host_os == "win"',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=win32',
+                '--no_auth',
+                '--bucket', 'chromium-clang-format',
+                '-s', 'buildtools/win/clang-format.exe.sha1',
+    ],
+  },
+  {
+    'name': 'clang_format_mac',
+    'pattern': '.',
+    'condition': 'host_os == "mac"',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=darwin',
+                '--no_auth',
+                '--bucket', 'chromium-clang-format',
+                '-s', 'buildtools/mac/clang-format.sha1',
+    ],
+  },
+  {
+    'name': 'clang_format_linux',
+    'pattern': '.',
+    'condition': 'host_os == "linux"',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=linux*',
+                '--no_auth',
+                '--bucket', 'chromium-clang-format',
+                '-s', 'buildtools/linux64/clang-format.sha1',
+    ],
+  },
+
+  # Pull the compilers and system libraries for hermetic builds
+  {
+    'name': 'sysroot_x86',
+    'pattern': '.',
+    'condition': 'checkout_linux and ((checkout_x86 or checkout_x64))',
+    'action': ['python', 'build/linux/sysroot_scripts/install-sysroot.py',
+               '--arch=x86'],
+  },
+  {
+    'name': 'sysroot_x64',
+    'pattern': '.',
+    'condition': 'checkout_linux and (checkout_x64)',
+    'action': ['python', 'build/linux/sysroot_scripts/install-sysroot.py',
+               '--arch=x64'],
+  },
+  {
+    # Update the Windows toolchain if necessary. Must run before 'clang' below.
+    'name': 'win_toolchain',
+    'pattern': '.',
+    'condition': 'checkout_win',
+    'action': ['python', 'build/vs_toolchain.py', 'update', '--force'],
+  },
+  {
+    # Note: On Win, this should run after win_toolchain, as it may use it.
+    'name': 'clang',
+    'pattern': '.',
+    'action': ['python', 'tools/clang/scripts/update.py'],
+  },
+  {
+    # Pull rc binaries using checked-in hashes.
+    'name': 'rc_win',
+    'pattern': '.',
+    'condition': 'checkout_win and (host_os == "win")',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--no_auth',
+                '--bucket', 'chromium-browser-clang/rc',
+                '-s', 'build/toolchain/win/rc/win/rc.exe.sha1',
+    ],
+  },
+  # Pull binutils for linux hermetic builds
+  {
+    'name': 'binutils',
+    'pattern': 'src/third_party/binutils',
+    'condition': 'host_os == "linux"',
+    'action': [
+        'python',
+        'third_party/binutils/download.py',
+    ],
+  },
+  # Update build/util/LASTCHANGE.
+  {
+    'name': 'lastchange',
+    'pattern': '.',
+    'action': ['python', 'build/util/lastchange.py',
+               '-o', 'build/util/LASTCHANGE'],
+  },
+]
+
+recursedeps = [
+  # buildtools provides clang_format, libc++, and libc++abi
+  'buildtools',
+]