Fixing chromium MSVC64(dbg) build.

CL https://webrtc-review.googlesource.com/c/src/+/28120 removed a
public dependency from rtc_tools:video_quality_analysis on
common_video:common_video.

This was keeping the MSVC64(dbg) build green because was giving the
linker the opportunity to find api:optional symbols.

This CL tries to fix and adds a TODO to remove the synthetic
dependency. The dependency on api:optional should be added to
rtc_base:rtc_base_approved_generic but this triggers another
dependency cycle.

TBR=tommi@webrtc.org

Bug: webrtc:6828
Change-Id: I4e28b49fdb3ee6484a253ca7b1f1a8aafa20e915
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/29683
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21079}

rtc_tools/BUILD.gn

@@ -65,6 +65,13 @@ rtc_static_library("video_quality_analysis") {
   ]
   deps = [
     "$rtc_libyuv_dir",
+
+    # TODO(bugs.webrtc.org/6828): api:optional should be a dependency
+    # of rtc_base:rtc_base_approved_generic but that causes a circular
+    # dependency. In order to fix the chromium build on MSVC64 (dbg)
+    # this dependency has to be added here so the linker can find the
+    # symbols it needs.
+    "../api:optional",
   ]
 }