Makes assert_selection() to set focus to sample IFRAME

This patch makes |assert_selection()| to set focus to sample IFRAME to ensure
|eventSender| and |testRunner.execCommand()| to work on sample IFRAME rather
than main frame.

The expectation sample of "editing/deleting/delete_by_word.html" is changed to
"Ctrl+Backspace", delete by word, deletes word before caret. Before this
patch, "Ctrl+Backspace" was sent to main frame and sample IFRAME didn't handle
it and did nothing.

BUG=n/a
TEST=n/a; no behavior changes

Review-Url: https://codereview.chromium.org/2341563003
Cr-Commit-Position: refs/heads/master@{#418524}

third_party/WebKit/LayoutTests/editing/assert_selection.js

@@ -554,6 +554,9 @@ class Sample {
     this.selection_.document.offsetTop = this.iframe_.offsetTop;
     this.selection_.setClipboardData = setClipboardData;
 
+    // Set focus to sample IFRAME to make |eventSender| and
+    // |testRunner.execCommand()| to work on sample rather than main frame.
+    this.iframe_.focus();
     this.load(sampleText);
   }
 

third_party/WebKit/LayoutTests/editing/deleting/delete_by_word.html

@@ -19,10 +19,9 @@
                 eventSender.keyDown('Backspace', kDeleteWordModifiers);
                 selection.document.execCommand('insertText', false, ' cha');
             },
-            // BR is a placeholder.
             [
                 '<div contenteditable>',
-                    'one two \u{00A0}abc cha|cha cha three four cha cha cha',
+                    'one two \u{00A0} cha|cha cha three four cha cha cha',
                 '</div>',
             ].join(''));
         }, 'Delete word');
@@ -39,10 +38,11 @@
                 eventSender.keyDown('Backspace', kDeleteWordModifiers);
                 selection.document.execCommand('undo');
             },
-            // BR is a placeholder.
             [
                 '<div contenteditable>',
-                    'one two |three four',
+                    isMac
+                        ? 'one |two ^three four'
+                        : 'one two |three four',
                 '</div>',
             ].join(''));
         }, 'Delete word then undo');