Fix ui/gl/BUILD.gn include_dirs Nonempty List Replacement Error

This change fixes this error:
ERROR at //ui/gl/BUILD.gn:236:7: Replacing nonempty list.
      include_dirs = [ "//third_party/swiftshader/include" ]
      ^-----------
This overwrites a previously-defined nonempty list (length 1).
See //ui/gl/BUILD.gn:132:18: for previous definition
  include_dirs = [ "//third_party/mesa/src/include" ]
                 ^----------------------------------
with another one (length 1). Did you mean "+=" to append instead? If you
really want to do this, do
  foo = []
before reassigning.
See //BUILD.gn:298:7: which caused the file to be included.
      "//ui/gl:gl_unittests",
      ^---------------------

BUG=635702
TBR=kylechar@chromium.org,piman@chromium.org,sievers@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2228803002
Cr-Commit-Position: refs/heads/master@{#410518}
1 file changed