[Content Index] Define mojo interface for the Content Index API

Define the mojo file, with an empty browser implementation, and pipe the
available blink calls to it.

Bug: 973844
Change-Id: Ife0d4a1b6a01ee3f8964f82227752c01207fe1a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660655
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Richard Knoll <[email protected]>
Reviewed-by: Peter Beverloo <[email protected]>
Reviewed-by: Tom Sepez <[email protected]>
Reviewed-by: Avi Drissman <[email protected]>
Commit-Queue: Rayan Kanso <[email protected]>
Cr-Commit-Position: refs/heads/master@{#670875}
diff --git a/third_party/blink/public/mojom/BUILD.gn b/third_party/blink/public/mojom/BUILD.gn
index d53a3e5..12570ff 100644
--- a/third_party/blink/public/mojom/BUILD.gn
+++ b/third_party/blink/public/mojom/BUILD.gn
@@ -31,6 +31,7 @@
     "clipboard/clipboard.mojom",
     "commit_result/commit_result.mojom",
     "contacts/contacts_manager.mojom",
+    "content_index/content_index.mojom",
     "cookie_store/cookie_store.mojom",
     "crash/crash_memory_metrics_reporter.mojom",
     "credentialmanager/credential_manager.mojom",