Migrate GpuProcess to use MojoChild/ShellConnection for the Shell handshake

Extracted from: https://codereview.chromium.org/2096643002/

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BUG=

Review-Url: https://codereview.chromium.org/2104553002
Cr-Commit-Position: refs/heads/master@{#402381}
diff --git a/content/BUILD.gn b/content/BUILD.gn
index 2193f545..3ab32ff 100644
--- a/content/BUILD.gn
+++ b/content/BUILD.gn
@@ -116,6 +116,7 @@
   ]
   deps = [
     "//content/public/app:browser_manifest",
+    "//content/public/app:gpu_manifest",
     "//content/public/app:renderer_manifest",
     "//services/catalog:manifest",
   ]