Add p7zip to install-build-deps.sh.

It's only needed for win/cross builds, but it's a small package and the
only additional package needed for cross builds, so add it unconditionally.

Change a/chrome/tools/build/win/create_installer_archive.py to use
7zr instead of 7za (both suffice for us), so that the smaller p7zip is enough.

Bug: 495204
Change-Id: I5f4c5326dbab2f3a3257c8cad4d3524cb338fca6
Reviewed-on: https://chromium-review.googlesource.com/934686
Reviewed-by: Thomas Anderson <[email protected]>
Commit-Queue: Nico Weber <[email protected]>
Cr-Commit-Position: refs/heads/master@{#538828}
diff --git a/build/install-build-deps.sh b/build/install-build-deps.sh
index df6ed90..fb1a1cb 100755
--- a/build/install-build-deps.sh
+++ b/build/install-build-deps.sh
@@ -200,6 +200,7 @@
   libxtst-dev
   locales
   openbox
+  p7zip
   patch
   perl
   pkg-config