Bug 1667887: fix Remove Dead Code in HighContrastCheck in the Screenshots UI r=emalysz

Differential Revision: https://phabricator.services.mozilla.com/D112263

browser/extensions/screenshots/build/inlineSelectionCss.js

@@ -253,9 +253,11 @@ window.inlineSelectionCss = `
     position: absolute;
     inset-inline-end: 0;
     top: 0; }
-  body.hcm .hover-highlight {
-    background-color: white;
-    opacity: 0.2; }
+    /* When prefers contrast is fully supported, we should change these quereies to cover both high and low prefers contrast cases */
+    @media (forced-colors: active) {
+      .hover-highlight {
+        background-color: white;
+        opacity: 0.2; } }
 
 .mover-target.direction-topLeft {
   cursor: nwse-resize;
@@ -357,9 +359,11 @@ window.inlineSelectionCss = `
   background-color: rgba(0, 0, 0, 0.7);
   position: absolute;
   z-index: 9999999999; }
-  body.hcm .bghighlight {
-    background-color: black;
-    opacity: 0.7; }
+  /* When prefers contrast is fully supported, we should change these quereies to cover both high and low prefers contrast cases */
+  @media (forced-colors: active) {
+    .bghighlight {
+      background-color: black;
+      opacity: 0.7; } }
 
 .preview-overlay {
   align-items: center;
@@ -374,9 +378,11 @@ window.inlineSelectionCss = `
   top: 0;
   width: 100%;
   z-index: 9999999999; }
-  body.hcm .preview-overlay {
-    background-color: black;
-    opacity: 0.7; }
+  /* When prefers contrast is fully supported, we should change these quereies to cover both high and low prefers contrast cases */
+  @media (forced-colors: active) {
+    .preview-overlay {
+      background-color: black;
+      opacity: 0.7; } }
 
 .precision-cursor {
   cursor: crosshair; }
@@ -388,9 +394,11 @@ window.inlineSelectionCss = `
   cursor: move;
   position: absolute;
   z-index: 9999999999; }
-  body.hcm .highlight {
-    border: 2px dashed white;
-    opacity: 1.0; }
+  /* When prefers contrast is fully supported, we should change these quereies to cover both high and low prefers contrast cases */
+  @media (forced-colors: active) {
+    .highlight {
+      border: 2px dashed white;
+      opacity: 1.0; } }
 
 .highlight-buttons {
   display: flex;

browser/extensions/screenshots/selector/ui.js

@@ -58,19 +58,6 @@ this.ui = (function() {
     );
   }
 
-  function highContrastCheck(win) {
-    const doc = win.document;
-    const el = doc.createElement("div");
-    el.style.backgroundImage = "url('#')";
-    el.style.display = "none";
-    doc.body.appendChild(el);
-    const computed = win.getComputedStyle(el);
-    doc.body.removeChild(el);
-    // When Windows is in High Contrast mode, Firefox replaces background
-    // image URLs with the string "none".
-    return computed && computed.backgroundImage === "none";
-  }
-
   function initializeIframe() {
     const el = document.createElement("iframe");
     el.src = browser.extension.getURL("blank.html");
@@ -150,9 +137,6 @@ this.ui = (function() {
       catcher.watchPromise(
         callBackground("sendEvent", "internal", "unhide-selection-frame")
       );
-      if (highContrastCheck(this.element.contentWindow)) {
-        this.element.contentDocument.body.classList.add("hcm");
-      }
       this.initSizeWatch();
       this.element.focus();
     },
@@ -362,9 +346,6 @@ this.ui = (function() {
       catcher.watchPromise(
         callBackground("sendEvent", "internal", "unhide-preselection-frame")
       );
-      if (highContrastCheck(this.element.contentWindow)) {
-        this.element.contentDocument.body.classList.add("hcm");
-      }
       this.element.focus();
     },