Fix editing/selection/mouse/mouse-selection-*.html on Mac

Now force windows editing behavior.

TBR=xiaochengh@chromium.org

Bug: 966731
Change-Id: I8af3aa3ae0744e6e2a650002eae47fc77b6f88fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1646889Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666598}

third_party/blink/web_tests/editing/selection/mouse/mouse-selection-horizontal.html

@@ -20,6 +20,10 @@ div {
 <!-- 40 Xs, 4 lines -->
 <div id="div">XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX</div>
 <script>
+// The expectations are based on windows editing behavior.
+if (window.internals)
+  internals.settings.setEditingBehavior('win');
+
 var node = div.firstChild;
 testMouseSelection(590, 310, 530, 310, node, 5, node, 35,
                    'Middle of the first line -> Middle of the last line');

third_party/blink/web_tests/editing/selection/mouse/mouse-selection-vertical-lr.html

@@ -20,6 +20,10 @@ div {
 <!-- 40 Xs, 4 lines -->
 <div id="div">XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX</div>
 <script>
+// The expectations are based on windows editing behavior.
+if (window.internals)
+  internals.settings.setEditingBehavior('win');
+
 var node = div.firstChild;
 testMouseSelection(210, 310, 270, 310, node, 5, node, 35,
                    'Middle of the first line -> Middle of the last line');

third_party/blink/web_tests/editing/selection/mouse/mouse-selection-vertical-rl.html

@@ -20,6 +20,10 @@ div {
 <!-- 40 Xs, 4 lines -->
 <div id="div">XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX</div>
 <script>
+// The expectations are based on windows editing behavior.
+if (window.internals)
+  internals.settings.setEditingBehavior('win');
+
 var node = div.firstChild;
 testMouseSelection(590, 310, 530, 310, node, 5, node, 35,
                    'Middle of the first line -> Middle of the last line');