layout: Don't pretend inline fragment sizes are zero when placing them

between floats.

components/gfx/text/text_run.rs

@@ -272,7 +272,14 @@ impl<'a> TextRun {
         })
     }
 
-    /// Returns the index of the first glyph run containing the given byte index.
+    pub fn minimum_splittable_inline_size(&self, range: &Range<ByteIndex>) -> Au {
+        match self.natural_word_slices_in_range(range).next() {
+            None => Au(0),
+            Some(slice) => self.advance_for_range(&slice.range),
+        }
+    }
+
+    /// Returns the index of the first glyph run containing the given character index.
     fn index_of_first_glyph_run_containing(&self, index: ByteIndex) -> Option<usize> {
         let self_ptr = self as *const TextRun;
         INDEX_OF_FIRST_GLYPH_RUN_CACHE.with(|index_of_first_glyph_run_cache| {

components/layout/fragment.rs

@@ -1471,6 +1471,17 @@ impl Fragment {
         result
     }
 
+    /// Returns the narrowest inline-size that the first splittable part of this fragment could
+    /// possibly be split to. (In most cases, this returns the inline-size of the first word in
+    /// this fragment.)
+    pub fn minimum_splittable_inline_size(&self) -> Au {
+        match self.specific {
+            SpecificFragmentInfo::ScannedText(ref text) => {
+                text.run.minimum_splittable_inline_size(&text.range)
+            }
+            _ => Au(0),
+        }
+    }
 
     /// TODO: What exactly does this function return? Why is it Au(0) for
     /// `SpecificFragmentInfo::Generic`?

components/layout/inline.rs

@@ -444,7 +444,7 @@ impl LineBreaker {
         // Initially, pretend a splittable fragment has zero inline-size. We will move it later if
         // it has nonzero inline-size and that causes problems.
         let placement_inline_size = if first_fragment.can_split() {
-            Au(0)
+            first_fragment.minimum_splittable_inline_size()
         } else {
             first_fragment.margin_box_inline_size() + self.indentation_for_pending_fragment()
         };