MacViews/a11y: Allow accessibility clients to set new selections in Textfields.

ui/views/widget/native_widget_mac_accessibility_unittest.mm

 // Copyright 2016 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 <memory>
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 393 matching lines @@
   new_string = base::SysUTF16ToNSString(front + replacement + back);
   textfield->SelectRange(test_range);
   [ax_node accessibilitySetValue:base::SysUTF16ToNSString(replacement)
                     forAttribute:NSAccessibilitySelectedTextAttribute];
   EXPECT_NSEQ(new_string,
               AttributeValueAtMidpoint(NSAccessibilityValueAttribute));
   EXPECT_EQ(base::SysNSStringToUTF16(new_string), textfield->text());
   // Make sure the cursor is at the end of the replacement.
   EXPECT_EQ(gfx::Range(front.length() + replacement.length()),
             textfield->GetSelectedRange());
+
+  EXPECT_TRUE([ax_node accessibilityIsAttributeSettable:
+                           NSAccessibilitySelectedTextRangeAttribute]);
+  // Check it's still possible to change the selection range when read-only.
+  textfield->SetReadOnly(true);
+  EXPECT_TRUE([ax_node accessibilityIsAttributeSettable:
+                           NSAccessibilitySelectedTextRangeAttribute]);
+
+  // Change the selection to a valid range within the text.
+  [ax_node accessibilitySetValue:[NSValue valueWithRange:NSMakeRange(2, 5)]
+                    forAttribute:NSAccessibilitySelectedTextRangeAttribute];
+  EXPECT_EQ(gfx::Range(2, 7), textfield->GetSelectedRange());
+  // If the length is longer than the value length, default to the max possible.
+  [ax_node accessibilitySetValue:[NSValue valueWithRange:NSMakeRange(0, 1000)]
+                    forAttribute:NSAccessibilitySelectedTextRangeAttribute];
+  EXPECT_EQ(gfx::Range(0, textfield->text().length()),
+            textfield->GetSelectedRange());
+  // Check just moving the cursor works, too.
+  [ax_node accessibilitySetValue:[NSValue valueWithRange:NSMakeRange(5, 0)]
+                    forAttribute:NSAccessibilitySelectedTextRangeAttribute];
+  EXPECT_EQ(gfx::Range(5, 5), textfield->GetSelectedRange());
 }
 
 }  // namespace views