canonicalize rustc::session import

Cargo.lock

@@ -3787,6 +3787,7 @@ dependencies = [
  "rustc_hir",
  "rustc_index",
  "rustc_parse",
+ "rustc_session",
  "rustc_span",
  "rustc_target",
  "syntax",

src/librustc_passes/Cargo.toml

@@ -17,6 +17,7 @@ rustc_feature = { path = "../librustc_feature" }
 rustc_hir = { path = "../librustc_hir" }
 rustc_index = { path = "../librustc_index" }
 rustc_parse = { path = "../librustc_parse" }
+rustc_session = { path = "../librustc_session" }
 rustc_target = { path = "../librustc_target" }
 syntax = { path = "../libsyntax" }
 rustc_span = { path = "../librustc_span" }

src/librustc_passes/ast_validation.rs

@@ -7,10 +7,10 @@
 // or type checking or some other kind of complex analysis.
 
 use rustc::lint;
-use rustc::session::Session;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{struct_span_err, Applicability, FatalError};
 use rustc_parse::validate_attr;
+use rustc_session::Session;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym};
 use rustc_span::Span;