Add ppapi, improve Windows GN build.

build/config/win/BUILD.gn

Index: build/config/win/BUILD.gn
diff --git a/build/config/win/BUILD.gn b/build/config/win/BUILD.gn
index 9738fff142f8bfab4bf20a8437c897455f761c66..8f08e4fcdd36dd46a14560075a1802c88e83470f 100644
--- a/build/config/win/BUILD.gn
+++ b/build/config/win/BUILD.gn
@@ -15,7 +15,6 @@ config("sdk") {
     "_WIN32_WINNT=0x0602",
     "_WINDOWS",
     "CERT_CHAIN_PARA_HAS_EXTRA_FIELDS",
-    "NOMINMAX",
     "NTDDI_VERSION=0x06020000",
     "PSAPI_VERSION=1",
     "WIN32",
@@ -129,3 +128,15 @@ config("lean_and_mean") {
     "WIN32_LEAN_AND_MEAN",
   ]
 }
+
+# Nominmax --------------------------------------------------------------------
+
+# Some third party code defines NOMINMAX before including windows.h, which
+# then causes warnings when it's been previously defined on the command line.
+# For such targets, this config can be removed.
+
+config("nominmax") {
+  defines = [
+    "NOMINMAX",
+  ]
+}