Implemented SetSelection for the Web content on Windows.

content/browser/accessibility/browser_accessibility_cocoa.mm

Index: content/browser/accessibility/browser_accessibility_cocoa.mm
diff --git a/content/browser/accessibility/browser_accessibility_cocoa.mm b/content/browser/accessibility/browser_accessibility_cocoa.mm
index 2142d7f8d24837b34036475e9881249671f3ec09..be5a3560b782ba5a124922925f385f79e0a2ff64 100644
--- a/content/browser/accessibility/browser_accessibility_cocoa.mm
+++ b/content/browser/accessibility/browser_accessibility_cocoa.mm
@@ -959,8 +959,7 @@ NSString* const NSAccessibilityRequiredAttribute = @"AXRequired";
   if (!root)
     return nil;
 
-  AXPlatformPositionInstance position =
-      CreateTextPosition(*root, 0, ui::AX_TEXT_AFFINITY_DOWNSTREAM);
+  AXPlatformPositionInstance position = root->CreatePositionAt(0);
   return CreateTextMarker(position->CreatePositionAtEndOfAnchor());
 }
 
@@ -1719,8 +1718,7 @@ NSString* const NSAccessibilityRequiredAttribute = @"AXRequired";
   if (!root)
     return nil;
 
-  AXPlatformPositionInstance position =
-      CreateTextPosition(*root, 0, ui::AX_TEXT_AFFINITY_DOWNSTREAM);
+  AXPlatformPositionInstance position = root->CreatePositionAt(0);
   return CreateTextMarker(position->CreatePositionAtStartOfAnchor());
 }
 
@@ -2128,8 +2126,8 @@ NSString* const NSAccessibilityRequiredAttribute = @"AXRequired";
   }
 
   if ([attribute isEqualToString:@"AXTextMarkerRangeForUIElement"]) {
-    AXPlatformPositionInstance startPosition = CreateTextPosition(
-        *browserAccessibility_, 0, ui::AX_TEXT_AFFINITY_DOWNSTREAM);
+    AXPlatformPositionInstance startPosition =
+        browser_accessibility_->CreatePositionAt(0);
     AXPlatformPositionInstance endPosition =
         startPosition->CreatePositionAtEndOfAnchor();
     AXPlatformRange range =