Revamped DropRange data structure

Not currently working. Need to flow drop information.

Author: eholk

Cargo.lock

@@ -4383,7 +4383,6 @@ dependencies = [
 name = "rustc_typeck"
 version = "0.0.0"
 dependencies = [
- "itertools 0.9.0",
  "rustc_arena",
  "rustc_ast",
  "rustc_attr",
@@ -4396,6 +4395,7 @@ dependencies = [
  "rustc_lint",
  "rustc_macros",
  "rustc_middle",
+ "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",

compiler/rustc_typeck/Cargo.toml

@@ -8,7 +8,6 @@ test = false
 doctest = false
 
 [dependencies]
-itertools = "0.9"
 rustc_arena = { path = "../rustc_arena" }
 tracing = "0.1"
 rustc_macros = { path = "../rustc_macros" }
@@ -28,3 +27,4 @@ rustc_infer = { path = "../rustc_infer" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_ty_utils = { path = "../rustc_ty_utils" }
 rustc_lint = { path = "../rustc_lint" }
+rustc_serialize = { path = "../rustc_serialize" }