Disable WebViewAPITest.AcceptTouchEvents on Linux.

This test exhibits flaky failures on Linux. Example:

https://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29/builds/34099

BUG=422998
TBR=hanxi@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/649243003

Cr-Commit-Position: refs/heads/master@{#299317}

extensions/browser/guest_view/web_view/web_view_apitest.cc

@@ -271,7 +271,13 @@ content::WebContents* WebViewAPITest::GetGuestWebContents() {
   return GetGuestViewManager()->WaitForSingleGuestCreated();
 }
 
-IN_PROC_BROWSER_TEST_F(WebViewAPITest, AcceptTouchEvents) {
+// Occasionally hits NOTIMPLEMENTED on Linux.  https://crbug.com/422998
+#if defined(OS_LINUX)
+#define MAYBE_AcceptTouchEvents DISABLED_AcceptTouchEvents
+#else
+#define MAYBE_AcceptTouchEvents AcceptTouchEvents
+#endif
+IN_PROC_BROWSER_TEST_F(WebViewAPITest, MAYBE_AcceptTouchEvents) {
   LaunchApp("web_view/accept_touch_events");
 
   content::RenderViewHost* embedder_rvh =