Revert of Temporarily remove chrome_app_unittests from the Dr. Memory builder...

Revert of Temporarily remove chrome_app_unittests from the Dr. Memory builder (patchset #1 id:1 of https://codereview.chromium.org/2278113002/ )

Reason for revert:
Reverting, because Dr. Memory test bots need that executable. It didn't break until a clobber landed and deleted the executable generated in the past.

Also glider@ reports that chrome_app_unittests was probably innocent (in the bug report) anyways.

First breaking build: https://build.chromium.org/p/chromium.memory.full/builders/Windows%20Unit%20%28DrMemory%20full%29%20%285%29/builds/130

Original issue's description:
> Temporarily remove chrome_app_unittests from the Dr. Memory builder
>
> BUG=640185
> TBR=dpranke@chromium.org
> NOTRY=true
>
> Committed: https://crrev.com/ad1aac65be3a92db6e76bf62336569ee65246666
> Cr-Commit-Position: refs/heads/master@{#414420}

TBR=dpranke@chromium.org,glider@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=640185

Review-Url: https://codereview.chromium.org/2347223002
Cr-Commit-Position: refs/heads/master@{#419220}

testing/buildbot/chromium.full.json

@@ -96,6 +96,7 @@
       "install_static_unittests",
       "keyboard_unittests",
       "unit_tests",
+      "chrome_app_unittests",
       "libaddressinput_unittests",
       "libphonenumber_unittests",
       "content_browsertests",