Add `operator<=` to checked iterators.

Bug: 817982
Change-Id: Ice97de84ed3e45ea4c237e953a80a5817c5d53b4
Reviewed-on: https://chromium-review.googlesource.com/c/1372893
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629100}

base/containers/checked_iterators.h

@@ -57,6 +57,11 @@ class CheckedRandomAccessIterator {
     return current_ < other.current_;
   }
 
+  bool operator<=(const CheckedRandomAccessIterator& other) const {
+    CheckComparable(other);
+    return current_ <= other.current_;
+  }
+
   CheckedRandomAccessIterator& operator++() {
     CHECK(current_ != end_);
     ++current_;
@@ -205,6 +210,11 @@ class CheckedRandomAccessConstIterator {
     return current_ < other.current_;
   }
 
+  bool operator<=(const CheckedRandomAccessConstIterator& other) const {
+    CheckComparable(other);
+    return current_ <= other.current_;
+  }
+
   CheckedRandomAccessConstIterator& operator++() {
     CHECK(current_ != end_);
     ++current_;