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The GLIB_DISABLE_DEPRECATION_WARNINGS define disables the deprecation
warnings which is caused by the usage of the g_settings_list_schemas
method. Moving the define to the build scripts avoids any future build
errors (-Werror) and warning reports.

BUG=391250
TEST=ninja -C out/Release chrome

Review URL: https://codereview.chromium.org/367113004

Cr-Commit-Position: refs/heads/master@{#292608}