Disable flaky AccessibilityActionBrowserTest.ImgElementGetImage on Mac

TBR=yaoxia@chromium.org

Bug: 1047921
Change-Id: I5883ab91335fb7faa0a7ee45d93b5535b2cca794
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033513Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737708}

content/browser/accessibility/accessibility_action_browsertest.cc

@@ -346,7 +346,14 @@ IN_PROC_BROWSER_TEST_F(AccessibilityCanvasActionBrowserTest,
   EXPECT_EQ(SK_ColorMAGENTA, bitmap.getColor(3, 1));
 }
 
-IN_PROC_BROWSER_TEST_F(AccessibilityActionBrowserTest, ImgElementGetImage) {
+// Flaky on Mac, crbug.com/1047921
+#if defined(OS_MACOSX)
+#define MAYBE_ImgElementGetImage DISABLED_ImgElementGetImage
+#else
+#define MAYBE_ImgElementGetImage ImgElementGetImage
+#endif
+IN_PROC_BROWSER_TEST_F(AccessibilityActionBrowserTest,
+                       MAYBE_ImgElementGetImage) {
   EXPECT_TRUE(NavigateToURL(shell(), GURL(url::kAboutBlankURL)));
 
   AccessibilityNotificationWaiter waiter(shell()->web_contents(),