Put the chrome://crash/rust C++ bindings in the blink namespace

C++ symbols in blink should all be in the blink namespace, putting them
in the top level namespace was an accident.

The callers are in the blink namespace too, so no change to the C++
callers was needed.

Change-Id: Ibb3e46a4103f3264178876eb795f0e3a91ea9eb2
Cq-Include-Trybots: luci.chromium.try:android-rust-arm32-rel,android-rust-arm64-dbg,android-rust-arm64-rel,linux-rust-x64-dbg,linux-rust-x64-rel,mac-rust-x64-dbg,win-rust-x64-dbg,win-rust-x64-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4706517
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1173694}

third_party/blink/common/rust_crash/src/lib.rs

@@ -5,7 +5,7 @@
 //! Code to generate an artificial Rust panic to exercise our crash handling
 //! logic and ensure it works for Rust crashes.
 
-#[cxx::bridge]
+#[cxx::bridge(namespace = "blink")]
 mod ffi {
     extern "Rust" {
         fn crash_in_rust(); // step 1 of main crash trigger. We bounce back to C++