DevTools: Fix TextPrompt expression calculation

Without shadow dom, the shadow-TextPrompt, the _proxyElement now contains a <style> tag

Bug: 934813
Change-Id: I5e3c9f33b94bae244587e549d6869055f08ee833
Reviewed-on: https://chromium-review.googlesource.com/c/1490193
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635806}

third_party/blink/renderer/devtools/front_end/ui/TextPrompt.js

@@ -415,7 +415,7 @@ UI.TextPrompt = class extends Common.Object {
 
     const expressionRange = wordQueryRange.cloneRange();
     expressionRange.collapse(true);
-    expressionRange.setStartBefore(this._proxyElement);
+    expressionRange.setStartBefore(this._element);
     const completionRequestId = ++this._completionRequestId;
     const completions = await this._loadCompletions(expressionRange.toString(), wordQueryRange.toString(), !!force);
     this._completionsReady(completionRequestId, selection, wordQueryRange, !!force, completions);

third_party/blink/web_tests/http/tests/devtools/unit/text-prompt-expected.txt

@@ -15,3 +15,8 @@ Test with disableDefaultSuggestionForEmptyInput
 Text:
 TextWithCurrentSuggestion:
 
+Test expression and query
+Text:the expression and query
+Expression:the expression and 
+Query:query
+

third_party/blink/web_tests/http/tests/devtools/unit/text-prompt.js

@@ -3,7 +3,12 @@
 
   var suggestions = ["heyoo", "hey it's a suggestion", "hey another suggestion"].map(s => ({text: s}));
   var prompt = new UI.TextPrompt();
-  prompt.initialize(() => Promise.resolve(suggestions));
+  let expression, query;
+  prompt.initialize(async (e, q) => {
+    expression = e;
+    query = q;
+    return suggestions;
+  });
   var div = document.createElement("div");
   UI.inspectorView.element.appendChild(div);
   prompt.attachAndStartEditing(div);
@@ -32,5 +37,13 @@
   TestRunner.addResult("Text:" + prompt.text());
   TestRunner.addResult("TextWithCurrentSuggestion:" + prompt.textWithCurrentSuggestion());
 
+  TestRunner.addResult("\nTest expression and query")
+  prompt.setText("the expression and query");
+  await prompt.complete();
+  TestRunner.addResult("Text:" + prompt.text());
+  TestRunner.addResult("Expression:" + expression);
+  TestRunner.addResult("Query:" + query);
+
+
   TestRunner.completeTest();
 })();