Show stack traces in console for unhandled promise rejection messages.

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;
@@ skipping 54 matching lines @@
 
 InspectorTest.fixConsoleViewportDimensions = function(width, height)
 {
     var viewport = WebInspector.ConsolePanel._view()._viewport;
     viewport.element.style.width = width + "px";
     viewport.element.style.height = height + "px";
     viewport.element.style.position = "absolute";
     viewport.invalidate();
 }
 
+InspectorTest.consoleMessagesCount = function()
+{
+    var consoleView = WebInspector.ConsolePanel._view();
+    return consoleView._consoleMessages.length;
+}
+
 InspectorTest.dumpConsoleMessages = function(printOriginatingCommand, dumpClassNames, formatter)
 {
     InspectorTest.addResults(InspectorTest.dumpConsoleMessagesIntoArray(printOriginatingCommand, dumpClassNames, formatter));
 }
 
 InspectorTest.dumpConsoleMessagesIntoArray = function(printOriginatingCommand, dumpClassNames, formatter)
 {
     formatter = formatter || InspectorTest.prepareConsoleMessageText;
     var result = [];
     InspectorTest.disableConsoleViewport();
@@ skipping 185 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();
 }
 
 }