Auto merge of #26697 - utsavoza:ugo/issue-11681/22-05-2020, r=jdm

Implement CanvasRenderingContext2d.fillText

The PR consists of broadly two main changes:
- Implementation of Canvas2dRenderingContext.font
- Basic implementation of Canvas2dRenderingContext.fillText

Although I am not fully sure about the long term goals for the canvas backend in Servo, I assumed limited scope for font and text handling (should support simple text drawing with font selection) in the current implementation as I believe a more complete implementation would eventually be brought in as a part of #22957.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #11681
- [x] There are tests for these changes

components/layout_2020/query.rs

@@ -21,12 +21,14 @@ use script_layout_interface::wrapper_traits::{
 };
 use script_traits::LayoutMsg as ConstellationMsg;
 use script_traits::UntrustedNodeAddress;
+use servo_arc::Arc as ServoArc;
 use std::collections::HashMap;
 use std::sync::{Arc, Mutex};
 use style::computed_values::position::T as Position;
 use style::context::{StyleContext, ThreadLocalStyleContext};
 use style::dom::OpaqueNode;
 use style::dom::TElement;
+use style::properties::style_structs::Font;
 use style::properties::{LonghandId, PropertyDeclarationId, PropertyId};
 use style::selector_parser::PseudoElement;
 use style::stylist::RuleInclusion;
@@ -65,6 +67,9 @@ pub struct LayoutThreadData {
     /// A queued response for the resolved style property of an element.
     pub resolved_style_response: String,
 
+    /// A queued response for the resolved font style for canvas.
+    pub resolved_font_style_response: Option<ServoArc<Font>>,
+
     /// A queued response for the offset parent/rect of a node.
     pub offset_parent_response: OffsetParentResponse,
 
@@ -139,6 +144,12 @@ impl LayoutRPC for LayoutRPCImpl {
         ResolvedStyleResponse(rw_data.resolved_style_response.clone())
     }
 
+    fn resolved_font_style(&self) -> Option<ServoArc<Font>> {
+        let &LayoutRPCImpl(ref rw_data) = self;
+        let rw_data = rw_data.lock().unwrap();
+        rw_data.resolved_font_style_response.clone()
+    }
+
     fn offset_parent(&self) -> OffsetParentResponse {
         let &LayoutRPCImpl(ref rw_data) = self;
         let rw_data = rw_data.lock().unwrap();
@@ -376,3 +387,11 @@ pub fn process_element_inner_text_query<'dom>(_node: impl LayoutNode<'dom>) -> S
 pub fn process_text_index_request(_node: OpaqueNode, _point: Point2D<Au>) -> TextIndexResponse {
     TextIndexResponse(None)
 }
+
+pub fn process_resolved_font_style_query<'dom>(
+    _node: impl LayoutNode<'dom>,
+    _property: &PropertyId,
+    _value: &str,
+) -> Option<ServoArc<Font>> {
+    None
+}