Chromium: Add a section about the chromium::import! macro. (#1611)

src/SUMMARY.md

@@ -255,6 +255,7 @@
 - [Testing](chromium/testing.md)
   - [`rust_gtest_interop` Library](chromium/testing/rust-gtest-interop.md)
   - [GN Rules for Rust Tests](chromium/testing/build-gn.md)
+  - [`chromium::import!` Macro](chromium/testing/chromium-import-macro.md)
   - [Exercise](exercises/chromium/testing.md)
 - [Interoperability with C++](chromium/interoperability-with-cpp.md)
   - [Example Bindings](chromium/interoperability-with-cpp/example-bindings.md)

src/chromium/testing/chromium-import-macro.md

@@ -0,0 +1,40 @@
+# `chromium::import!` Macro
+
+After adding `:my_rust_lib` to GN `deps`, we still need to learn how to import
+and use `my_rust_lib` from `my_rust_lib_unittest.rs`.  We haven't provided an
+explicit `crate_name` for `my_rust_lib` so its crate name is computed based on
+the full target path and name. Fortunately we can avoid working with such an
+unwieldy name by using the `chromium::import!` macro from the
+automatically-imported `chromium` crate:
+
+```rust,ignore
+chromium::import! {
+    "//ui/base:my_rust_lib";
+}
+
+use my_rust_lib::my_function_under_test;
+```
+
+Under the covers the macro expands to something similar to:
+
+```rust,ignore
+extern crate ui_sbase_cmy_urust_ulib as my_rust_lib;
+
+use my_rust_lib::my_function_under_test;
+```
+
+More information can be found in [the doc comment][0] of the `chromium::import`
+macro.
+
+<details>
+
+`rust_static_library` supports specifying an explicit name via `crate_name`
+property, but doing this is discouraged.  And it is discouraged because
+the crate name has to be globally unique.  crates.io guarantees uniqueness
+of its crate names so `cargo_crate` GN targets (generated by the `gnrt`
+tool covered in a later section) use short crate names.
+
+</details>
+
+
+[0]: https://source.chromium.org/chromium/chromium/src/+/main:build/rust/chromium_prelude/chromium_prelude.rs?q=f:chromium_prelude.rs%20pub.use.*%5Cbimport%5Cb;%20-f:third_party&ss=chromium%2Fchromium%2Fsrc

src/exercises/chromium/third-party.md

@@ -28,7 +28,7 @@ more than that, they probably forgot to turn off the default features.
 
 Thanks to [Daniel Liu][3] for this crate!
 
-</detail>
+</details>
 
 
 [0]: https://crates.io/crates/uwuify