Harmonize paths to dependent targets.

This CL consistently use:
 * relative paths for WebRTC dependent targets (test_support)
 * absolute paths for shared dependent targets (abseil)
This is a necessary (but insufficient) step to build WebRTC tests
from Chromium tree (rtc_include_tests=true), since test/ doesn't
sit anymore in the top level directory.

We also make sure that target declarations and uses are
consistent in regard to build_with_chromium flag.

Bug: webrtc:9943
Bug: webrtc:9855
Change-Id: I21dea98894df2fd4bfe2fd7ee7b71ba971e0ab5b
Reviewed-on: https://webrtc-review.googlesource.com/c/108720
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Yves Gerey <yvesg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25445}
diff --git a/modules/audio_coding/BUILD.gn b/modules/audio_coding/BUILD.gn
index f36e4f0..455dcd0 100644
--- a/modules/audio_coding/BUILD.gn
+++ b/modules/audio_coding/BUILD.gn
@@ -1500,7 +1500,7 @@
              "../../rtc_base/system:arch",
              "../../test:test_main",
              "//testing/gtest",
-             "//test:test_support",
+             "../../test:test_support",
            ] + audio_coding_deps
 
     data = audio_decoder_unittests_resources
@@ -1618,8 +1618,8 @@
       "../../api:libjingle_peerconnection_api",
       "../../rtc_base:rtc_base_approved",
       "../../test:test_main",
+      "../../test:test_support",
       "../audio_processing",
-      "//test:test_support",
       "//testing/gtest",
     ]
   }
@@ -1980,7 +1980,7 @@
       "../../rtc_base:rtc_base_approved",
       "../../test:fileutils",
       "../../test:test_main",
-      "//test:test_support",
+      "../../test:test_support",
       "//testing/gtest",
     ]
   }