Drop less output of actool from compile_xcassets.py.

Change compile_xcassets.py to keep all output in known sections
(except com.apple.actool.compilation-results) as some errors do
not follow the pattern that was used, discarding the compilation
error message.

Bug: 739163
Change-Id: Ide40508913e5d32111ad9ba2225745d67465023b
Reviewed-on: https://chromium-review.googlesource.com/563298
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#485164}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c8ddaa9787cdff766f819c402d2dcd6de796fa90
2 files changed