IDL files should also use LF line endings.

Existing files are all fine because of a presubmit enforcing this, but setting
gitattributes makes it easier to not trigger the presubmit in the first place.

Bug: 832129
Change-Id: I3e82d89196d28d23c609e5e1ded56817505da0e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1635868
Auto-Submit: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664542}

.gitattributes

@@ -15,6 +15,7 @@
 *.gni text eol=lf
 *.h text eol=lf
 *.html   text eol=lf
+*.idl text eol=lf
 *.in   text eol=lf
 *.inc   text eol=lf
 *.java   text eol=lf