Remove OSMesa from the chromium repo

Now that SwiftShader has been integrated into every platform on every test,
we can remove OSMesa from the chromium codebase.

BUG=chromium:873321

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_chromium_dbg_ng;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ie75c73c172aaffd17a3e041aa7f4cf37a96c3d4d
Reviewed-on: https://chromium-review.googlesource.com/1128207
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Mohsen Izadi <mohsen@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Cait Phillips <caitkp@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582655}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index a70ef19..ea03f18 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -552,7 +552,7 @@
   ]
   if (!is_android) {
     data_deps = [
-      "//third_party/mesa:osmesa",
+      "//third_party/mesa_headers",
     ]
   }
 }
@@ -751,9 +751,8 @@
     "//ui/gl",
     "//ui/gl:test_support",
   ]
-
   data_deps = [
-    "//third_party/mesa:osmesa",
+    "//third_party/mesa_headers",
   ]
 }