Revert "[Extensions] Revert changes to icon loading JS function."

This reverts commit e80df6f2.

Reason for revert: seems to have broken builder "Network Service Linux"

Original change's description:
> [Extensions] Revert changes to icon loading JS function.
> 
> Bug: 1049214
> Change-Id: I64018260d06070da03821bbcb72578de62359be3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042313
> Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
> Commit-Queue: David Bertoni <dbertoni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#739076}

TBR=lazyboy@chromium.org,dbertoni@chromium.org

Change-Id: I4cf9a417bdf5b13aad77d6a4cb054a27dbe6a42f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1049214, 1049467
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2043003Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Commit-Queue: Carlos Knippschild <carlosk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739198}

extensions/renderer/resources/set_icon.js

@@ -5,22 +5,32 @@
 var SetIconCommon = requireNative('setIcon').SetIconCommon;
 
 function loadImagePath(path, callback) {
-  var img = new Image();
-  img.onerror = function() {
-    console.error('Could not load action icon \'' + path + '\'.');
-  };
-  img.onload = function() {
-    var canvas = document.createElement('canvas');
-    canvas.width = img.width;
-    canvas.height = img.height
+  let fetchPromise = fetch(path);
+
+  let blobPromise = $Promise.then(fetchPromise, function(response) {
+    if (!response.ok) {
+      throw new $Error.self('Could not load action icon \'' + path + '\'.');
+    }
+    return response.blob();
+  });
+
+  let imagePromise = $Promise.then(blobPromise, function(blob) {
+    return createImageBitmap(blob);
+  });
+
+  let imageDataPromise = $Promise.then(imagePromise, function(image) {
+    var canvas = new OffscreenCanvas(image.width, image.height);
     var canvas_context = canvas.getContext('2d');
     canvas_context.clearRect(0, 0, canvas.width, canvas.height);
-    canvas_context.drawImage(img, 0, 0, canvas.width, canvas.height);
+    canvas_context.drawImage(image, 0, 0, canvas.width, canvas.height);
     var imageData = canvas_context.getImageData(0, 0, canvas.width,
                                                 canvas.height);
     callback(imageData);
-  };
-  img.src = path;
+  });
+
+  $Promise.catch(imageDataPromise, function(error) {
+    console.error(error);
+  });
 }
 
 function smellsLikeImageData(imageData) {