Deactivate dialog before taking screenshot

This should reduce the flakiness. Deactivated dialog pixel outputs
should be more predictable than activated dialog.
https://chrome-gold.skia.org/detail?test=BrowserUiDialog_TabGroupEditorBubbleViewDialogBrowserTest_InvokeUi_default&digest=45c8d0767462989beefdc816a729c3ad
https://chrome-gold.skia.org/detail?test=BrowserUiDialog_TabGroupEditorBubbleViewDialogBrowserTest_InvokeUi_default&digest=f0f4b37daa5fc41c5481163af8fc079e

Bug: 1059469
Change-Id: I1f7ebe20b4c58d4ba7481e4bcba9b177b205b91b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095769
Commit-Queue: Sven Zheng <svenzheng@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748565}

chrome/browser/ui/test/test_browser_dialog.cc

@@ -114,7 +114,10 @@ bool TestBrowserDialog::VerifyUi() {
 #if !defined(OS_MACOSX)
   if (pixel_diff_) {
     dialog_widget->SetBlockCloseForTesting(true);
-    dialog_widget->Activate();
+    // Deactivate before taking screenshot. Deactivated dialog pixel outputs
+    // is more predictable than activated dialog.
+    bool is_active = dialog_widget->IsActive();
+    dialog_widget->Deactivate();
     base::ScopedClosureRunner unblock_close(
         base::BindOnce(&views::Widget::SetBlockCloseForTesting,
                        base::Unretained(dialog_widget), false));
@@ -131,6 +134,8 @@ bool TestBrowserDialog::VerifyUi() {
       DLOG(INFO) << "VerifyUi(): Pixel compare failed.";
       return false;
     }
+    if (is_active)
+      dialog_widget->Activate();
   }
 #endif  // OS_MACOSX