[webkit] Bump garnet version

To fix web_view builder, so that a new webkit can be built, because the
new toolchain has a breaking change that renders the old one
incompatible.

Change-Id: I36e13fb7cc2c1f6dc1f9de61093dc247eb82732e
diff --git a/webkit b/webkit
index be23f41..ae2dc52 100644
--- a/webkit
+++ b/webkit
@@ -4,7 +4,7 @@
     <import remote="https://fuchsia.googlesource.com/garnet"
             manifest="manifest/garnet"
             name="garnet"
-            revision="cb3d058029118350d6a0cc8b0887d0700be679cc"/>
+            revision="3dd9b6ff0ff03f23ed1750e0c04e1cfa00509297"/>
   </imports>
   <projects>
     <project name="third_party/webkit"