Compile the skia library for windows using gn.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index f14a027af5b090771d11880cf27b4ea7fd640818..361cd409e05e0a02b82ab716d79ea60f2d8379a2 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -404,6 +404,10 @@ component("skia") {
     ":xml",
   ]
 
+  if (!is_win) {

[mtklein, 2016/09/14 21:25:14]

Probably redundant.

[herb_g, 2016/09/16 19:54:15]

Done.

+    libs = [ "pthread" ]
+  }
+  
   sources = []
   sources += skia_core_sources
   sources += skia_effects_sources
@@ -469,7 +473,7 @@ component("skia") {
       "src/ports/SkTypeface_win_dw.cpp",
       "src/xps/SkDocument_XPS.cpp",
     ]
-    sources -= [ "src/utils/SkThreadUtils_pthread.cpp" ]
+    sources -= [ get_path_info("src/utils/SkThreadUtils_pthread.cpp", "abspath") ]
   } else {
     sources += [
       "src/ports/SkOSFile_posix.cpp",