Auto merge of #6876 - metajack:slice_chars-layout, r=pcwalton

Use local slice_chars

StrExt::slice_chars is deprecated and will be removed in Rust. This
lifts the implementation from Rust libstd and puts it in util::str.

This fixes a bunch of deprecation warnings in Servo.

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components/layout/fragment.rs

@@ -46,7 +46,7 @@ use url::Url;
 use util::geometry::{Au, ZERO_POINT};
 use util::logical_geometry::{LogicalRect, LogicalSize, LogicalMargin, WritingMode};
 use util::range::*;
-use util::str::is_whitespace;
+use util::str::{is_whitespace, slice_chars};
 use util;
 
 /// Fragments (`struct Fragment`) are the leaves of the layout tree. They cannot position
@@ -204,8 +204,8 @@ impl fmt::Debug for SpecificFragmentInfo {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             SpecificFragmentInfo::ScannedText(ref info) => {
-                write!(f, " \"{}\"", info.run.text.slice_chars(info.range.begin().get() as usize,
-                                                               info.range.end().get() as usize))
+                write!(f, " \"{}\"", slice_chars(&*info.run.text, info.range.begin().get() as usize,
+                                                 info.range.end().get() as usize))
             }
             _ => Ok(())
         }
@@ -2094,7 +2094,8 @@ impl Fragment {
 
         let mut leading_whitespace_character_count = 0;
         {
-            let text = scanned_text_fragment_info.run.text.slice_chars(
+            let text = slice_chars(
+                &*scanned_text_fragment_info.run.text,
                 scanned_text_fragment_info.range.begin().to_usize(),
                 scanned_text_fragment_info.range.end().to_usize());
             for character in text.chars() {

components/layout/inline.rs

@@ -35,6 +35,7 @@ use unicode_bidi;
 use util::geometry::{Au, MAX_AU, ZERO_RECT};
 use util::logical_geometry::{LogicalRect, LogicalSize, WritingMode};
 use util::range::{Range, RangeIndex};
+use util::str::slice_chars;
 use util;
 
 // From gfxFontConstants.h in Firefox
@@ -1801,7 +1802,7 @@ fn strip_trailing_whitespace_if_necessary(text_run: &TextRun, range: &mut Range<
     debug!("stripping trailing whitespace: range={:?}, len={}",
            range,
            text_run.text.chars().count());
-    let text = text_run.text.slice_chars(range.begin().to_usize(), range.end().to_usize());
+    let text = slice_chars(&*text_run.text, range.begin().to_usize(), range.end().to_usize());
     let mut trailing_whitespace_character_count = 0;
     for ch in text.chars().rev() {
         if util::str::char_is_whitespace(ch) {

components/layout/lib.rs

@@ -13,7 +13,6 @@
 #![feature(mpsc_select)]
 #![feature(plugin)]
 #![feature(raw)]
-#![feature(slice_chars)]
 #![feature(step_by)]
 #![feature(str_char)]
 #![feature(unsafe_no_drop_flag)]