Update deps to pull sdl

BUG=skia:

Review URL: https://codereview.chromium.org/1425033003
diff --git a/DEPS b/DEPS
index 489eb78..4544c10 100644
--- a/DEPS
+++ b/DEPS
@@ -41,6 +41,9 @@
   "third_party/externals/sfntly" : "https://chromium.googlesource.com/external/sfntly/cpp/src.git@1bdaae8fc788a5ac8936d68bf24f37d977a13dac",
   # ICU is needed for sfntly.
   "third_party/externals/icu" : "https://chromium.googlesource.com/chromium/deps/icu.git@ce41627e388fb46ab49671bd16a5db81dcd75a71",
+
+  # sdl will be needed for native windows
+  "third_party/externals/sdl" : "https://skia.googlesource.com/third_party/sdl@9b526d28cb2d7f0ccff0613c94bb52abc8f53b6f",
 }
 
 recursedeps = [ "common" ]