Share /gnu/store in the BubbleWrap container and remove FHS mounts.

This is a Guix-specific patch not meant to be upstreamed.
diff --git a/Source/WebKit/UIProcess/Launcher/glib/BubblewrapLauncher.cpp b/Source/WebKit/UIProcess/Launcher/glib/BubblewrapLauncher.cpp
index f0a5e4b05dff..88b11f806968 100644
--- a/Source/WebKit/UIProcess/Launcher/glib/BubblewrapLauncher.cpp
+++ b/Source/WebKit/UIProcess/Launcher/glib/BubblewrapLauncher.cpp
@@ -854,27 +854,12 @@ GRefPtr<GSubprocess> bubblewrapSpawn(GSubprocessLauncher* launcher, const Proces
         "--ro-bind", "/sys/dev", "/sys/dev",
         "--ro-bind", "/sys/devices", "/sys/devices",
 
-        "--ro-bind-try", "/usr/share", "/usr/share",
-        "--ro-bind-try", "/usr/local/share", "/usr/local/share",
         "--ro-bind-try", DATADIR, DATADIR,
-
-        // We only grant access to the libdirs webkit is built with and
-        // guess system libdirs. This will always have some edge cases.
-        "--ro-bind-try", "/lib", "/lib",
-        "--ro-bind-try", "/usr/lib", "/usr/lib",
-        "--ro-bind-try", "/usr/local/lib", "/usr/local/lib",
         "--ro-bind-try", LIBDIR, LIBDIR,
-#if CPU(ADDRESS64)
-        "--ro-bind-try", "/lib64", "/lib64",
-        "--ro-bind-try", "/usr/lib64", "/usr/lib64",
-        "--ro-bind-try", "/usr/local/lib64", "/usr/local/lib64",
-#else
-        "--ro-bind-try", "/lib32", "/lib32",
-        "--ro-bind-try", "/usr/lib32", "/usr/lib32",
-        "--ro-bind-try", "/usr/local/lib32", "/usr/local/lib32",
-#endif
-
         "--ro-bind-try", PKGLIBEXECDIR, PKGLIBEXECDIR,
+
+        // Bind mount the store inside the WebKitGTK sandbox.
+        "--ro-bind", "@storedir@", "@storedir@",
     };
 
     if (launchOptions.processType == ProcessLauncher::ProcessType::DBusProxy) {
nge</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=14a81366e285a58f147669984558fd1660398a45'>root</a>/<a href='/guix/log/tests?id=14a81366e285a58f147669984558fd1660398a45'>tests</a>/<a href='/guix/log/tests/cpio.scm?id=14a81366e285a58f147669984558fd1660398a45'>cpio.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/cpio.scm?id=14a81366e285a58f147669984558fd1660398a45&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/build/linux-initrd.scm?id=53a457e4a15c1e4a6d3474212bf54b8cede048a2&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-12-15 17:32:10 +0100'>2020-12-15</span></td><td><a href='/guix/commit/gnu/build/linux-initrd.scm?id=6a060ff27ff68384d7c90076baa36c349fff689d'>store-copy: 'populate-store' can optionally deduplicate files.</a><span class='msg-avail'>...<span class='msg-tooltip'>Until now deduplication was performed as an additional pass after
copying files, which involve re-traversing all the files that had just
been copied.

* guix/store/deduplication.scm (copy-file/deduplicate): New procedure.
* tests/store-deduplication.scm ("copy-file/deduplicate"): New test.
* guix/build/store-copy.scm (populate-store): Add #:deduplicate?
parameter and honor it.
* tests/gexp.scm ("gexp-&gt;derivation, store copy"): Pass #:deduplicate? #f
to 'populate-store'.
* gnu/build/image.scm (initialize-root-partition): Pass #:deduplicate?
to 'populate-store'.  Pass #:deduplicate? #f to 'register-closure'.
* gnu/build/vm.scm (root-partition-initializer): Likewise.
* gnu/build/install.scm (populate-single-profile-directory): Pass
 #:deduplicate? #f to 'populate-store'.
* gnu/build/linux-initrd.scm (build-initrd): Likewise.
* guix/scripts/pack.scm (self-contained-tarball)[import-module?]: New
procedure.
[build]: Pass it as an argument to 'source-module-closure'.
* guix/scripts/pack.scm (squashfs-image)[build]: Wrap in
'with-extensions'.
* gnu/system/linux-initrd.scm (expression-&gt;initrd)[import-module?]: New
procedure.
[builder]: Pass it to 'source-module-closure'.
* gnu/system/install.scm (cow-store-service-type)[import-module?]: New
procedure.  Pass it to 'source-module-closure'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-21 12:39:14 +0100'>2020-11-21</span></td><td><a href='/guix/commit/gnu/build/linux-initrd.scm?id=2200bb214690ebc78b9fa42887ac9dfb8035bd4f'>linux-initrd: Remove unnecessary timestamp reset phase.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/linux-initrd.scm (write-cpio-archive): Mention timestamps in
docstring.
(build-initrd): Remove unnecessary timestamp reset phase.
</span></span></td><td>Ludovic Courtès</td></tr>