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

chrome/browser/ui/find_bar/find_bar_host_browsertest.cc

Index: chrome/browser/ui/find_bar/find_bar_host_browsertest.cc
diff --git a/chrome/browser/ui/find_bar/find_bar_host_browsertest.cc b/chrome/browser/ui/find_bar/find_bar_host_browsertest.cc
index eb378be44f607d4e568ff57e3fb30b5d75e5f88e..45641451d00805594d502a28ee5933521b4efeba 100644
--- a/chrome/browser/ui/find_bar/find_bar_host_browsertest.cc
+++ b/chrome/browser/ui/find_bar/find_bar_host_browsertest.cc
@@ -750,6 +750,10 @@ IN_PROC_BROWSER_TEST_F(FindInPageControllerTest, FindMovesWhenObscuring) {
   // Search for something guaranteed not to be obscured by the Find box.
   EXPECT_EQ(1, FindInPageWchar(tab, L"Done",
                                kFwd, kIgnoreCase, &ordinal));
+
+  // Drain MessageLoop so that find bar position settles.
+  ui_test_utils::RunAllPendingInMessageLoop();
+
   // Check the position.
   EXPECT_TRUE(GetFindBarWindowInfo(&position, &fully_visible));
   EXPECT_TRUE(fully_visible);
@@ -766,6 +770,9 @@ IN_PROC_BROWSER_TEST_F(FindInPageControllerTest, FindMovesWhenObscuring) {
   EXPECT_EQ(0, FindInPageWchar(tab, L"WeirdSearchString",
                                kFwd, kIgnoreCase, &ordinal));
 
+  // Drain MessageLoop so that find bar position settles.
+  ui_test_utils::RunAllPendingInMessageLoop();
+
   // Check the position.
   EXPECT_TRUE(GetFindBarWindowInfo(&position, &fully_visible));
   EXPECT_TRUE(fully_visible);