Add base::RunLoop and update ui_test_utils to use it to reduce flakiness

base/message_loop.cc

Index: base/message_loop.cc
diff --git a/base/message_loop.cc b/base/message_loop.cc
index a207659a4a922203a2e3850bbcdde4b1425dd21d..7a6e0921cb09d1b91cb845b24a62a22ea9caf610 100644
--- a/base/message_loop.cc
+++ b/base/message_loop.cc
@@ -313,7 +313,7 @@ void MessageLoop::RunAllPending() {
   RunHandler();
 }
 
-void MessageLoop::Quit() {
+void MessageLoop::QuitWhenIdle() {
   DCHECK_EQ(this, current());
   if (state_) {
     state_->quit_received = true;
@@ -331,13 +331,40 @@ void MessageLoop::QuitNow() {
   }
 }
 
-static void QuitCurrent() {
-  MessageLoop::current()->Quit();
+void MessageLoop::QuitAfterPending() {
+  DCHECK_EQ(this, current());
+  if (state_) {
+    PostTask(FROM_HERE, MessageLoop::QuitNowClosure());
+  } else {
+    NOTREACHED() << "Must be inside Run to call Quit";
+  }
+}
+
+static void QuitWhenIdleCurrent() {
+  MessageLoop::current()->QuitWhenIdle();
+}
+
+static void QuitNowCurrent() {
+  MessageLoop::current()->QuitNow();
+}
+
+static void QuitAfterPendingCurrent() {
+  MessageLoop::current()->QuitAfterPending();
+}
+
+// static
+base::Closure MessageLoop::QuitWhenIdleClosure() {
+  return base::Bind(&QuitWhenIdleCurrent);
+}
+
+// static
+base::Closure MessageLoop::QuitNowClosure() {
+  return base::Bind(&QuitNowCurrent);
 }
 
 // static
-base::Closure MessageLoop::QuitClosure() {
-  return base::Bind(&QuitCurrent);
+base::Closure MessageLoop::QuitAfterPendingClosure() {
+  return base::Bind(&QuitAfterPendingCurrent);
 }
 
 void MessageLoop::SetNestableTasksAllowed(bool allowed) {