Update from https://crrev.com/308331

Fix ui/compositor/compositor.(h|cpp) based on http://crrev.com/738983002

Fix sky/engine based on current Blink code

R=qsr@chromium.org

Review URL: https://codereview.chromium.org/812543002
diff --git a/build/vs_toolchain.py b/build/vs_toolchain.py
index fb7e142..5373f03 100644
--- a/build/vs_toolchain.py
+++ b/build/vs_toolchain.py
@@ -202,7 +202,7 @@
       os.environ['WINDOWSSDKDIR'],
       os.environ['GYP_MSVS_VERSION'],
       os.environ.get('WDK_DIR', ''),
-      ';'.join(runtime_dll_dirs))
+      ';'.join(runtime_dll_dirs or ['None']))
 
 
 def main():