Revert "Disable flaky AccessibilityActionBrowserTest.ImgElementGetImage on Mac"

This reverts commit a05d328d.

Reason for revert: Flakiness should have been fixed by https://crrev.com/c/2035374

Original change's description:
> 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/+/2033513
> Reviewed-by: Marc Treib <treib@chromium.org>
> Commit-Queue: Marc Treib <treib@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#737708}

TBR=treib@chromium.org,yaoxia@chromium.org

Change-Id: Iafb9d0713816f66bb6f73ad20521b642dab7df97
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1047921
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033451Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737759}

content/browser/accessibility/accessibility_action_browsertest.cc

@@ -346,14 +346,7 @@ IN_PROC_BROWSER_TEST_F(AccessibilityCanvasActionBrowserTest,
   EXPECT_EQ(SK_ColorMAGENTA, bitmap.getColor(3, 1));
 }
 
-// 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) {
+IN_PROC_BROWSER_TEST_F(AccessibilityActionBrowserTest, ImgElementGetImage) {
   EXPECT_TRUE(NavigateToURL(shell(), GURL(url::kAboutBlankURL)));
 
   AccessibilityNotificationWaiter waiter(shell()->web_contents(),