Add mac SDK's size & llvm-size tools to sizes_test data.

Fails on swarming due to missing size, eg:
https://chrome-swarming.appspot.com/task?id=45909000afe02a10

R=erikchen, dpranke

Bug: 961548
Change-Id: I2ce40de235243f21e4b52b02c2925efade230fcd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1669979Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671468}

tools/binary_size/sizes.gni

@@ -33,6 +33,17 @@ template("sizes_test") {
         "--size-path",
         mac_bin_path + "size",
       ]
+
+      if (!defined(data)) {
+        data = []
+      }
+
+      # 'size' is a symlink to 'llvm-size', so throw both in there, but don't
+      # add the entire bin path since it's large.
+      data += [
+        mac_bin_path + "llvm-size",
+        mac_bin_path + "size",
+      ]
     }
   }
 }