Use visual studio toolchain from depot_tools for PDFium compilation

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 595da736ba8610dbb7c28a1eb3df0fb0330d6d1b..c33b02755ad1680cabcc92173d2e597bf3c3568c 100644
--- a/DEPS
+++ b/DEPS
@@ -143,4 +143,10 @@ hooks = [
     'pattern': '.',
     'action': ['python', 'pdfium/tools/clang/scripts/update.py', '--if-needed'],
   },
+  {
+    # Update the Windows toolchain if necessary.
+    'name': 'win_toolchain',
+    'pattern': '.',
+    'action': ['python', 'pdfium/build/vs_toolchain.py', 'update'],
+  },
 ]