DevTools: Migrate from -webkit-user-modify to contenteditable

third_party/WebKit/Source/devtools/front_end/ui/TextPrompt.js

Index: third_party/WebKit/Source/devtools/front_end/ui/TextPrompt.js
diff --git a/third_party/WebKit/Source/devtools/front_end/ui/TextPrompt.js b/third_party/WebKit/Source/devtools/front_end/ui/TextPrompt.js
index 3ef2086d504dce95ff224329a44c7429afebe49d..24b008cadd258c11f3af1b5e128b287aae58319e 100644
--- a/third_party/WebKit/Source/devtools/front_end/ui/TextPrompt.js
+++ b/third_party/WebKit/Source/devtools/front_end/ui/TextPrompt.js
@@ -216,6 +216,7 @@ UI.TextPrompt = class extends Common.Object {
    */
   _startEditing(blurListener) {
     this._isEditing = true;
+    this._element.setAttribute('contenteditable', 'plaintext-only');
     this._contentElement.classList.add('text-prompt-editing');
     if (blurListener) {
       this._blurListener = blurListener;
@@ -234,6 +235,7 @@ UI.TextPrompt = class extends Common.Object {
     if (this._blurListener)
       this._element.removeEventListener('blur', this._blurListener, false);
     this._contentElement.classList.remove('text-prompt-editing');
+    this._element.removeAttribute('contenteditable');
     delete this._isEditing;
   }