Enable touchpad fling bubbling test.

This cl enables BrowserSideFlingBrowserTest.TouchpadFlingBubblesFromOOPIF
to see if it still flakes or not.
I expect the test to be stable after the changes that landed in
https://chromium-review.googlesource.com/c/chromium/src/+/1289515

TBR=creis@chromium.org

Bug: 894703
Change-Id: I17164061e0d41886eb73537936cac94e61a91011
Reviewed-on: https://chromium-review.googlesource.com/c/1291811Reviewed-by: Sahel Sharify <sahel@chromium.org>
Commit-Queue: Sahel Sharify <sahel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601256}

content/browser/renderer_host/input/fling_browsertest.cc

@@ -355,9 +355,8 @@ IN_PROC_BROWSER_TEST_F(BrowserSideFlingBrowserTest,
   WaitForFrameScroll(GetRootNode(), 15, true /* upward */);
 }
 
-// Flaky, probably because of https://crbug.com/892656
 IN_PROC_BROWSER_TEST_F(BrowserSideFlingBrowserTest,
-                       DISABLED_TouchpadFlingBubblesFromOOPIF) {
+                       TouchpadFlingBubblesFromOOPIF) {
   LoadPageWithOOPIF();
   // Scroll the parent down so that it is scrollable upward.
   EXPECT_TRUE(