[COIL] Change chromium code search type links to use main rather than…

… master for fuchsia

    See this doc: go/chromium-coil-change for more info
    BUG=1210385

Change-Id: If84cbf58b9aad9b4a3ceea750f70007e933b476c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2902868
Auto-Submit: John Palmer <jopalmer@chromium.org>
Commit-Queue: Fabrice de Gans <fdegans@chromium.org>
Reviewed-by: Fabrice de Gans <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#884779}

fuchsia/DIR_METADATA

@@ -1,10 +1,10 @@
 # Metadata information for this directory.
 #
 # For more information on DIR_METADATA files, see:
-#   https://source.chromium.org/chromium/infra/infra/+/master:go/src/infra/tools/dirmd/README.md
+#   https://source.chromium.org/chromium/infra/infra/+/main:go/src/infra/tools/dirmd/README.md
 #
 # For the schema of this file, see Metadata message:
-#   https://source.chromium.org/chromium/infra/infra/+/master:go/src/infra/tools/dirmd/proto/dir_metadata.proto
+#   https://source.chromium.org/chromium/infra/infra/+/main:go/src/infra/tools/dirmd/proto/dir_metadata.proto
 
 monorail {
   component: "Fuchsia"