Parameterize the ui_resources location.

build/ui_resources_location.gypi

Index: build/ui_resources_location.gypi
diff --git a/build/ui_resources_location.gypi b/build/ui_resources_location.gypi
new file mode 100644
index 0000000000000000000000000000000000000000..700638c974923f289eaa0c762db3a73e1d99bc5b
--- /dev/null
+++ b/build/ui_resources_location.gypi
@@ -0,0 +1,11 @@
+{
+  'variables': {
+     # The generated paths gen/ui/ui_resources and gen/ui/ui_strings are
+     # being moved to gen/ui/resources and gen/ui/strings, respectively. But
+     # Blink relies on the location of ui_resources to link its unit tests.
+     # Two facilitate the two-sided patch, this variable indicates the
+     # one currently in use.
+     # TODO(brettw) remove this when the move is complete.
+     'ui_resources_gen_subdir': 'ui_resources',
+  },
+}