Fix accessibility hit testing issue on Mac

https://crrev.com/c/2117330 refactored accessibility hit testing to use
physical pixel coordinates consistently but overlooked the fact that
MacOS passes hit test points in device-independent coordinates. This CL
scales the input by device scale factor to compensate. Test will come in
a follow-up CL.

Bug: 1086819
AX-Relnotes: Fixes an issue with accessibility hit testing on the Mac.
Change-Id: I3fcc2cee34082e58d7fd38fdc219672680674095
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225334Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Kevin Babbitt <kbabbitt@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#773765}

content/browser/accessibility/browser_accessibility_cocoa.mm

@@ -29,6 +29,7 @@
 #include "content/browser/accessibility/browser_accessibility_position.h"
 #include "content/browser/accessibility/one_shot_accessibility_tree_search.h"
 #include "content/public/common/content_client.h"
+#include "content/public/common/use_zoom_for_dsf_policy.h"
 #include "third_party/blink/public/strings/grit/blink_strings.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/accessibility/ax_enum_util.h"
@@ -55,6 +56,7 @@ using content::BrowserAccessibilityDelegate;
 using content::BrowserAccessibilityManager;
 using content::BrowserAccessibilityManagerMac;
 using content::ContentClient;
+using content::IsUseZoomForDSFEnabled;
 using content::OneShotAccessibilityTreeSearch;
 using ui::AXNodeData;
 using ui::AXTreeIDRegistry;
@@ -3672,7 +3674,13 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
   screen_point +=
       manager->GetViewBoundsInScreenCoordinates().OffsetFromOrigin();
 
-  BrowserAccessibility* hit = manager->CachingAsyncHitTest(screen_point);
+  gfx::Point physical_pixel_point =
+      content::IsUseZoomForDSFEnabled()
+          ? screen_point
+          : ScaleToRoundedPoint(screen_point, manager->device_scale_factor());
+
+  BrowserAccessibility* hit =
+      manager->CachingAsyncHitTest(physical_pixel_point);
   if (!hit)
     return nil;