rust: Document NDK methods and expose `ATrace_isEnabled`

sdk-lib/src/main/rust/utils/target_ndk.rs

@@ -10,8 +10,28 @@ use libc::c_char;
 #[derive(WrapperApi)]
 #[allow(non_snake_case)]
 pub struct Api23 {
+    /// Returns true if tracing is enabled. Use this to avoid expensive computation only
+    /// necessary when tracing is enabled.
+    #[allow(non_snake_case)]
+    ATrace_isEnabled: unsafe extern "C" fn() -> bool,
+
+    /// Writes a tracing message to indicate that the given section of code has begun.
+    ///
+    /// This call must be followed by a corresponding call to [`ATrace_endSection`] on the
+    /// same thread.
+    ///
+    /// Note: At this time the vertical bar character `|` and newline character `\n` are
+    /// used internally by the tracing mechanism. If `sectionName` contains these
+    /// characters they will be replaced with a space character in the trace.
     #[allow(non_snake_case)]
     ATrace_beginSection: unsafe extern "C" fn(sectionName: *const c_char),
+
+    /// Writes a tracing message to indicate that a given section of code has ended.
+    ///
+    /// This call must be preceeded by a corresponding call to [`ATrace_beginSection`] on
+    /// the same thread. Calling this method will mark the end of the most recently begun
+    /// section of code, so care must be taken to ensure that `ATrace_beginSection` /
+    /// `ATrace_endSection` pairs are properly nested and called from the same thread.
     #[allow(non_snake_case)]
     ATrace_endSection: unsafe extern "C" fn(),
 }