DevTools: make sure scope variables do not throw exception

third_party/WebKit/Source/devtools/front_end/sources/JavaScriptSourceFrame.js

Index: third_party/WebKit/Source/devtools/front_end/sources/JavaScriptSourceFrame.js
diff --git a/third_party/WebKit/Source/devtools/front_end/sources/JavaScriptSourceFrame.js b/third_party/WebKit/Source/devtools/front_end/sources/JavaScriptSourceFrame.js
index 141eb0a9ef171b3d0d853e9044fb8d775fe5d7fb..ddd650ea2728074d820baa29bc619a4a0ee76366 100644
--- a/third_party/WebKit/Source/devtools/front_end/sources/JavaScriptSourceFrame.js
+++ b/third_party/WebKit/Source/devtools/front_end/sources/JavaScriptSourceFrame.js
@@ -765,7 +765,7 @@ WebInspector.JavaScriptSourceFrame.prototype = {
             for (var line of this._valueWidgets.keys())
                 toLine = Math.max(toLine, line + 1);
         }
-        if (fromLine >= toLine || toLine - fromLine > 500) {
+        if (fromLine >= toLine || toLine - fromLine > 500 || fromLine < 0 || toLine >= this.textEditor.linesCount) {
             this._clearValueWidgets();
             return;
         }