Add tracing_chrome crate by copy-pasting file

The file was taken unmodified from the following link, except for file attributes at the top: https://github.com/thoren-d/tracing-chrome/blob/7e2625ab4aeeef2f0ef9bde9d6258dd181c04472/src/lib.rs
Depending on the tracing-chrome crate from crates.io is unfortunately not possible since it depends on `tracing_core` which conflicts with rustc_private's `tracing_core` (meaning it would not be possible to use the [ChromeLayer] in a context that expects a [Layer] from from rustc_private's `tracing_core` version)

Author: Stypox

Cargo.lock

@@ -27,6 +27,7 @@ chrono = { version = "0.4.38", default-features = false }
 chrono-tz = "0.10"
 directories = "6"
 bitflags = "2.6"
+serde_json = { version = "1.0", optional = true }
 
 # Copied from `compiler/rustc/Cargo.toml`.
 # But only for some targets, it fails for others. Rustc configures this in its CI, but we can't
@@ -66,7 +67,7 @@ default = ["stack-cache"]
 genmc = []
 stack-cache = []
 stack-cache-consistency-check = ["stack-cache"]
-tracing = []
+tracing = ["serde_json"]
 
 [lints.rust.unexpected_cfgs]
 level = "warn"

Cargo.toml

@@ -8,3 +8,8 @@ imports_granularity = "Module"
 force_multiline_blocks = true
 match_arm_blocks = false
 match_arm_leading_pipes = "Preserve"
+
+ignore = [
+    # this file is copy-pasted from the tracing_chrome crate and should remain like the original
+    "src/trace/tracing_chrome.rs"
+]

rustfmt.toml

@@ -88,6 +88,7 @@ mod operator;
 mod provenance_gc;
 mod range_map;
 mod shims;
+mod trace;
 
 // Establish a "crate-wide prelude": we often import `crate::*`.
 // Make all those symbols available in the same place as our own.

src/lib.rs

@@ -0,0 +1 @@
+mod tracing_chrome;