Instead of guessing, compute center point of Guest View for test.

chrome/browser/apps/guest_view/web_view_browsertest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <queue>
 
 #include "base/location.h"
 #include "base/path_service.h"
 #include "base/process/process.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 2502 matching lines @@
   // Sync changes to compositor.
   ForceCompositorFrame();
 
   aura_webview->RequestFocus();
   // Verify that other_focusable_view can steal focus from aura_webview.
   EXPECT_TRUE(aura_webview->HasFocus());
   other_focusable_view->RequestFocus();
   EXPECT_TRUE(other_focusable_view->HasFocus());
   EXPECT_FALSE(aura_webview->HasFocus());
 
+  // Compute location of guest within embedder so we can more accurately
+  // target our touch event.
+  gfx::Rect guest_rect = GetGuestWebContents()->GetContainerBounds();
+  gfx::Point embedder_origin =
+      GetEmbedderWebContents()->GetContainerBounds().origin();
+  guest_rect.Offset(-embedder_origin.x(), -embedder_origin.y());
+
   // Generate and send synthetic touch event.
-  // TODO(wjmaclean): This is fragile ... if anyone alters the location/size
-  // of the webview in accept_touch_events then this may miss its target.
   FocusWaiter waiter(aura_webview);
-  content::SimulateTouchPressAt(GetEmbedderWebContents(), gfx::Point(10, 10));
+  content::SimulateTouchPressAt(GetEmbedderWebContents(),
+                                guest_rect.CenterPoint());
 
   // Wait for the TouchStart to propagate and restore focus. Test times out
   // on failure.
   waiter.Wait();
 }
 #endif