Enable gtk3 for 32-bit builds

build/config/linux/gtk/gtk.gni

Index: build/config/linux/gtk/gtk.gni
diff --git a/build/config/linux/gtk/gtk.gni b/build/config/linux/gtk/gtk.gni
index 0521a8cd48cdfc5d66871b11d1761c2fd5b984e7..53e943e14d29b6ac6223d07d5d1664fed461e0f4 100644
--- a/build/config/linux/gtk/gtk.gni
+++ b/build/config/linux/gtk/gtk.gni
@@ -8,8 +8,5 @@
 
 declare_args() {
   # Whether to compile against GTKv3 instead of GTKv2.
-  # TODO(thomasanderson): Currently, the 32-bit clusterfuzz schroot does not
-  # have libgtk-3-0 installed.  set use_gtk3 = true on all architectures when
-  # the package is added (crbug.com/699669).
-  use_gtk3 = target_cpu == "x64"
+  use_gtk3 = true
 }