Instrumented libraries: disallow loadable modules for gdk-pixbuf.

This eliminates a warning in the best case, a startup crash in the worst case.

BUG=456636
TBR=glider@chromim.org
NOTRY=true

Review URL: https://codereview.chromium.org/911963002

Cr-Commit-Position: refs/heads/master@{#315604}

third_party/instrumented_libraries/instrumented_libraries.gyp

@@ -626,6 +626,10 @@
           '--with-x11',
           # Make the build less problematic.
           '--disable-introspection',
+          # Do not use loadable modules. Same as with Pango, there's no easy way
+          # to make gdk-pixbuf pick instrumented versions over system-installed
+          # ones.
+          '--disable-modules',
       ],
       'dependencies=': [],
       'run_before_build': 'scripts/libgdk-pixbuf2.0-0.sh',