gn: Fix more build issues on Win

build/vs_toolchain.py

Index: build/vs_toolchain.py
diff --git a/build/vs_toolchain.py b/build/vs_toolchain.py
index 44c30171377d3045721b928faa3db6d0f55588a7..bdedd6fa8822f121da2687d338cbdf3f58140575 100644
--- a/build/vs_toolchain.py
+++ b/build/vs_toolchain.py
@@ -164,6 +164,13 @@ def GetToolchainDir():
   """Gets location information about the current toolchain (must have been
   previously updated by 'update'). This is used for the GN build."""
   SetEnvironmentAndGetRuntimeDllDirs()
+
+  # If WINDOWSSDKDIR is not set, search the default SDK path and set it.
+  if not 'WINDOWSSDKDIR' in os.environ:
+    default_sdk_path = 'C:\\Program Files (x86)\\Windows Kits\\8.0'
+    if os.path.isdir(default_sdk_path):
+      os.environ['WINDOWSSDKDIR'] = default_sdk_path
+
   print '''vs_path = "%s"
 sdk_path = "%s"
 vs_version = "%s"