Add TODOs for broken build code in aggregate_vector_icons.

These just reference the bug on the build issue.

BUG=535386
TBR=dpranke@chromium.org

Review URL: https://codereview.chromium.org/1617153002

Cr-Commit-Position: refs/heads/master@{#370765}

ui/gfx/BUILD.gn

@@ -569,6 +569,11 @@ action("aggregate_vector_icons") {
   ]
 
   args = [
+    # TODO(brettw) bug 535386: This should not take a directory as an input,
+    # but rather a response file listing the inputs or sometimes the build will
+    # be incorrect. In this case, Ninja won't be able to do proper dependency
+    # tracking since if a file is deleted, the command line will be the same
+    # and the action will not be re-run.
     "--working_directory=" + rebase_path("vector_icons/"),
     "--output_cc=" + rebase_path(vector_icons_cc_file, root_build_dir),
     "--output_h=" + rebase_path(vector_icons_h_file, root_build_dir),

ui/gfx/vector_icons/aggregate_vector_icons.py

@@ -9,6 +9,10 @@ import os
 import textwrap
 
 
+# TODO(brettw) bug 535386: This should not take a directory as an input, but
+# rather a response file listing the inputs or sometimes the build will be
+# incorrect.
+
 def AggregateVectorIcons(working_directory, output_cc, output_h):
   """Compiles all .icon files in a directory into two C++ files.