Add //chromecast dir to //media/gpu/visibility

Cast code needs to access
media::GpuVideoAcceleratorUtil::ConvertGpuToMediaEncodeProfiles

Bug: internal b/147798485
Test: gn check
Change-Id: I78e9f0cba452e608db23018cc921b9a842319562
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2109119Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Sandeep Vijayasekar <sandv@google.com>
Auto-Submit: Sandeep Vijayasekar <sandv@google.com>
Cr-Commit-Position: refs/heads/master@{#751540}

media/gpu/BUILD.gn

@@ -28,6 +28,7 @@ component("gpu") {
   # media-related content code should access //media/gpu.
   visibility = [
     "//chrome/gpu",
+    "//chromecast/*",
     "//components/arc/mojom:media",
     "//components/arc/video_accelerator",
     "//components/mirroring/service:mirroring_service",