Enable building pdf_use_skia in the standalone build.

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 11ce870301815e6d61fd20980719c7a4b2bfdde8..002109f717aa084b358ed89960aba2c125936465 100644
--- a/DEPS
+++ b/DEPS
@@ -1,5 +1,11 @@
 use_relative_paths = True
 
+vars = {
+  'chromium_git': 'https://chromium.googlesource.com',

[Tom Sepez, 2016/03/16 18:51:51]

As long as you are going to introduce vars, would you be kind enough to update
all of the code below to use an expression like at line 17?

[dsinclair, 2016/03/16 19:35:14]

Done.

+
+  'skia_revision': 'ed854fb897fa134f2f64738a75293502fdcf1af2'
+}
+
 deps = {
   "build/gyp":
     "https://chromium.googlesource.com/external/gyp",
@@ -7,14 +13,17 @@ deps = {
   "buildtools":
     "https://chromium.googlesource.com/chromium/buildtools.git@c2f259809d5ede3275df5ea0842f0431990c4f98",
 
+  "third_party/skia":

[Tom Sepez, 2016/03/16 18:51:51]

alphabetize, move to line 28

[dsinclair, 2016/03/16 19:35:13]

Apparently I can't spell.

+    Var('chromium_git') + '/skia.git' + '@' +  Var('skia_revision'),
+
   "testing/corpus":
-     "https://pdfium.googlesource.com/pdfium_tests@bafb069353f96d441c6a37786d18cd9f5407937f",
+    "https://pdfium.googlesource.com/pdfium_tests@bafb069353f96d441c6a37786d18cd9f5407937f",
 
   "testing/gmock":
-     "https://chromium.googlesource.com/external/googlemock.git@29763965ab52f24565299976b936d1265cb6a271",
+    "https://chromium.googlesource.com/external/googlemock.git@29763965ab52f24565299976b936d1265cb6a271",
 
   "testing/gtest":
-     "https://chromium.googlesource.com/external/googletest.git@8245545b6dc9c4703e6496d1efd19e975ad2b038",
+    "https://chromium.googlesource.com/external/googletest.git@8245545b6dc9c4703e6496d1efd19e975ad2b038",
 
   "tools/clang":
     "https://chromium.googlesource.com/chromium/src/tools/clang",