Fetch third_party/skia directly from canonical Skia git repo.

The current git repo is a googlesource-to-googlesource mirror, where
origin/HEAD is set to the wrong branch. Stop using it, like Chromium did
in https://crrev.com/429926, so roll-dep can work correctly.

Bug: chromium:1275239
Change-Id: I2fe0c334fbdb7ca165a46d7b2a78680af94db2d3
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/87491
Commit-Queue: Lei Zhang <thestig@chromium.org>
Commit-Queue: Hui Yingst <nigi@chromium.org>
Reviewed-by: Hui Yingst <nigi@chromium.org>
diff --git a/DEPS b/DEPS
index faae9e7..9c3be7b 100644
--- a/DEPS
+++ b/DEPS
@@ -21,6 +21,7 @@
 
   'chromium_git': 'https://chromium.googlesource.com',
   'pdfium_git': 'https://pdfium.googlesource.com',
+  'skia_git': 'https://skia.googlesource.com',
 
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling abseil
@@ -258,7 +259,7 @@
         Var('nasm_source_revision'),
 
   'third_party/skia':
-    Var('chromium_git') + '/skia.git@' +  Var('skia_revision'),
+    Var('skia_git') + '/skia.git@' + Var('skia_revision'),
 
   'third_party/test_fonts':
     Var('chromium_git') + '/chromium/src/third_party/test_fonts.git@' +