DevTools: make ElementsTreeOutline shadow dom-based.

LayoutTests/http/tests/inspector/console-test.js

 var initialize_ConsoleTest = function() {
 
 InspectorTest.preloadPanel("console");
 
 InspectorTest.evaluateInConsole = function(code, callback)
 {
     callback = InspectorTest.safeWrap(callback);
 
     var consoleView = WebInspector.ConsolePanel._view();
     consoleView.visible = true;
     consoleView._prompt.text = code;
     var event = document.createEvent("KeyboardEvent");
     event.initKeyboardEvent("keydown", true, true, null, "Enter", "");
     consoleView._prompt.proxyElement.dispatchEvent(event);
     InspectorTest.addConsoleViewSniffer(function(commandResult) {
-        callback(commandResult.toMessageElement().textContent);
+        callback(commandResult.toMessageElement().deepTextContent());
     });
 }
 
 InspectorTest.addConsoleViewSniffer = function(override, opt_sticky)
 {
     var sniffer = function (viewMessage) {
         override(viewMessage);
     };
 
     InspectorTest.addSniffer(WebInspector.ConsoleView.prototype, "_consoleMessageAddedForTest", sniffer, opt_sticky);
 }
 
 InspectorTest.evaluateInConsoleAndDump = function(code, callback)
 {
     callback = InspectorTest.safeWrap(callback);
 
     function mycallback(text)
     {
         InspectorTest.addResult(code + " = " + text);
         callback(text);
     }
     InspectorTest.evaluateInConsole(code, mycallback);
 }
 
 InspectorTest.prepareConsoleMessageText = function(messageElement, consoleMessage)
 {
-    var messageText = messageElement.textContent.replace(/\u200b/g, "");
+    var messageText = messageElement.deepTextContent().replace(/\u200b/g, "");
     // Replace scriptIds with generic scriptId string to avoid flakiness.
     messageText = messageText.replace(/VM\d+/g, "VM");
     // Strip out InjectedScript line numbers from stack traces to avoid rebaselining each time InjectedScriptSource is edited.
     messageText = messageText.replace(/VM:\d+ InjectedScript\./g, " InjectedScript.");
     // Strip out InjectedScript line numbers from console message anchor.
     var functionName = consoleMessage && consoleMessage.stackTrace && consoleMessage.stackTrace[0] && consoleMessage.stackTrace[0].functionName || "";
     if (functionName.indexOf("InjectedScript") !== -1)
         messageText = messageText.replace(/\bVM:\d+/, ""); // Only first replace.
     if (messageText.startsWith("Navigated to")) {
         var fileName = messageText.split(" ").pop().split("/").pop();
@@ skipping 202 matching lines @@
     }
     if (!option) {
         InspectorTest.addResult("FAILED: context with prefix: "  + namePrefix + " not found in the context list");
         return;
     }
     option.selected = true;
     WebInspector.ConsolePanel._view()._executionContextChanged();
 }
 
 }