When doing a component build, some test binaries link against the object
files directly, bypassing the components. This results, however, and
rightly so, in linker warnings. In gyp, we just suppressed them. During
the transition to gn, this was dropped for two binaries.

Here I add the suppressions back in.

Long term, we should either change the tests to go through the public
API, or export the required symbols.

BUG=chromium:633688
R=jkummerow@chromium.org

Review-Url: https://codereview.chromium.org/2261123003
Cr-Commit-Position: refs/heads/master@{#38793}