Bug 1853124 - [devtools] Avoid changing cursor location when scrolling to first character. r=devtools-reviewers,bomsy

For some reason, the previous changeset triggers an additional call to `scrollToColumn`
during `open-large-minified-file` DAMP test, only on try but not locally.

Calling `codeMirror.charCoords` can be slow on large files and we often
try to scroll to the first line/first column. Let's arbitrarily scroll
to top/left when this simple case happens.

Differential Revision: https://phabricator.services.mozilla.com/D188443

devtools/client/debugger/src/utils/editor/index.js

@@ -88,6 +88,13 @@ export function toSourceLine(sourceId, line) {
 }
 
 export function scrollToPosition(codeMirror, line, column) {
+  // For all cases where these are on the first line and column,
+  // avoid the possibly slow computation of cursor location on large bundles.
+  if (!line && !column) {
+    codeMirror.scrollTo(0, 0);
+    return;
+  }
+
   const { top, left } = codeMirror.charCoords({ line, ch: column }, "local");
 
   if (!isVisible(codeMirror, top, left)) {