Initial import of itertools-0.9.0.

Bug: 155309706
Change-Id: Id790c146e836f0eadfb0d8a103cbe2d226a598c3

src/impl_macros.rs

diff --git a/src/impl_macros.rs b/src/impl_macros.rs
new file mode 100644
index 0000000..04ab8e1
--- /dev/null
+++ b/src/impl_macros.rs
@@ -0,0 +1,24 @@
+//! 
+//! Implementation's internal macros
+
+macro_rules! debug_fmt_fields {
+    ($tyname:ident, $($($field:ident).+),*) => {
+        fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            f.debug_struct(stringify!($tyname))
+                $(
+              .field(stringify!($($field).+), &self.$($field).+)
+              )*
+              .finish()
+        }
+    }
+}
+
+macro_rules! clone_fields {
+    ($($field:ident),*) => {
+        fn clone(&self) -> Self {
+            Self {
+                $($field: self.$field.clone(),)*
+            }
+        }
+    }
+}