Auto merge of #11914 - notriddle:text_fragment_color_merge, r=jdm

Text fragment color merge

The display list item for a line of text has a single color assigned for
it, so text fragments with different colors cannot be merged.

There is no issue number for this, as far as I know. I found this while
trying an internal program that uses red asterisks for required text
fields.
____________________

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not fix an existing Github issue
- [X] There are tests for these changes OR

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components/layout/construct.rs

@@ -949,7 +949,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
 
         // Modify the style as necessary. (See the comment in
         // `properties::modify_style_for_replaced_content()`.)
-        let mut style = (*node.style(self.style_context())).clone();
+        let mut style = node.style(self.style_context()).clone();
         properties::modify_style_for_replaced_content(&mut style);
 
         // If this is generated content, then we need to initialize the accumulator with the

components/layout/fragment.rs

@@ -38,9 +38,9 @@ use std::collections::LinkedList;
 use std::fmt;
 use std::sync::{Arc, Mutex};
 use style::computed_values::content::ContentItem;
-use style::computed_values::{border_collapse, clear, display, mix_blend_mode, overflow_wrap};
-use style::computed_values::{overflow_x, position, text_decoration, transform_style};
-use style::computed_values::{vertical_align, white_space, word_break, z_index};
+use style::computed_values::{border_collapse, clear, color, display, mix_blend_mode};
+use style::computed_values::{overflow_wrap, overflow_x, position, text_decoration};
+use style::computed_values::{transform_style, vertical_align, white_space, word_break, z_index};
 use style::dom::TRestyleDamage;
 use style::logical_geometry::{LogicalMargin, LogicalRect, LogicalSize, WritingMode};
 use style::properties::{ComputedValues, ServoComputedValues};
@@ -1304,6 +1304,10 @@ impl Fragment {
         self.style().get_inheritedtext().white_space
     }
 
+    pub fn color(&self) -> color::T {
+        self.style().get_color().color
+    }
+
     /// Returns the text decoration of this fragment, according to the style of the nearest ancestor
     /// element.
     ///
@@ -2042,7 +2046,8 @@ impl Fragment {
                 // FIXME: Should probably use a whitelist of styles that can safely differ (#3165)
                 if self.style().get_font() != other.style().get_font() ||
                         self.text_decoration() != other.text_decoration() ||
-                        self.white_space() != other.white_space() {
+                        self.white_space() != other.white_space() ||
+                        self.color() != other.color() {
                     return false
                 }