Add SK_IGNORE_WIN_EMOJI_FIX Skia build flag.

A fix for color emoji bounds on Windows is about to land in Skia but
will affect three layout tests. This flag will suppress the Skia change
until it is possible to rebaseline.

BUG=chromium:698492

Change-Id: I716e47b0fba0921a8fe9779aab071000a3960d7e
Reviewed-on: https://chromium-review.googlesource.com/1102488Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Ben Wagner <bungeman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567655}

skia/BUILD.gn

@@ -138,6 +138,9 @@ config("skia_library_config") {
     "//third_party/skia/src/lazy",
     "//third_party/skia/third_party/gif",
   ]
+
+  defines += [ "SK_IGNORE_WIN_EMOJI_FIX" ]
+
   if (is_mac || is_ios) {
     include_dirs += [ "//third_party/skia/include/utils/mac" ]
   }