Add some missing components_unittests to GN build.

This is about half of the missing tests.

Also converts some static libraries to source sets.

Review URL: https://codereview.chromium.org/1284403004

Cr-Commit-Position: refs/heads/master@{#344308}
diff --git a/components/audio_modem/BUILD.gn b/components/audio_modem/BUILD.gn
index 53f50f38..32f39637 100644
--- a/components/audio_modem/BUILD.gn
+++ b/components/audio_modem/BUILD.gn
@@ -24,6 +24,7 @@
     "//base",
     "//content",
     "//media",
+    "//media:shared_memory_support",
     "//third_party/webrtc/common_audio",
   ]
 }