Share line breaking state across text runs

Fixes #874

components/layout/fragment.rs

@@ -479,6 +479,11 @@ bitflags! {
 
         /// Is this fragment selected?
         const SELECTED = 0x02;
+
+        /// Suppress line breaking between this and the previous fragment
+        ///
+        /// This handles cases like Foo<span>bar</span>
+        const SUPPRESS_LINE_BREAK_BEFORE = 0x04;
     }
 }
 
@@ -1421,6 +1426,14 @@ impl Fragment {
         }
     }
 
+    pub fn suppress_line_break_before(&self) -> bool {
+        match self.specific {
+            SpecificFragmentInfo::ScannedText(ref st) =>
+                st.flags.contains(ScannedTextFlags::SUPPRESS_LINE_BREAK_BEFORE),
+            _ => false,
+        }
+    }
+
     /// Computes the intrinsic inline-sizes of this fragment.
     pub fn compute_intrinsic_inline_sizes(&mut self) -> IntrinsicISizesContribution {
         let mut result = self.style_specified_intrinsic_inline_size();
@@ -1621,6 +1634,16 @@ impl Fragment {
         }
     }
 
+    /// Does this fragment start on a glyph run boundary?
+    pub fn is_on_glyph_run_boundary(&self) -> bool {
+        let text_fragment_info = match self.specific {
+            SpecificFragmentInfo::ScannedText(ref text_fragment_info)
+                => text_fragment_info,
+            _   => return true,
+        };
+        text_fragment_info.run.on_glyph_run_boundary(text_fragment_info.range.begin())
+    }
+
     /// Truncates this fragment to the given `max_inline_size`, using a character-based breaking
     /// strategy. The resulting fragment will have `SpecificFragmentInfo::TruncatedFragment`,
     /// preserving the original fragment for use in incremental reflow.