-[WebHTMLView attributedSubstringForProposedRange:actualRange:] does not include strikethrough attribute in the returned attributed string
https://bugs.webkit.org/show_bug.cgi?id=119099
<rdar://problem/13439291>

Reviewed by Enrica Casucci.

Source/WebCore: 

Tests:
    API Test: AttributedStringTest_Strikethrough

* platform/mac/HTMLConverter.mm:
(+[WebHTMLConverter editingAttributedStringFromRange:]):
Set the NSStrikethroughStyleAttributeName attribute when text-decoration: line-through is seen.

Tools: 

* TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj:
* TestWebKitAPI/Tests/mac/AttributedString.mm:
(TestWebKitAPI::attributedString):
(TestWebKitAPI::AttributedStringTest_CustomFont::didLoadURL):
(TestWebKitAPI::AttributedStringTest_CustomFont::url):
(TestWebKitAPI::AttributedStringTest_CustomFont::runTest):
(TestWebKitAPI::TEST_F):
(TestWebKitAPI::AttributedStringTest_Strikethrough::didLoadURL):
(TestWebKitAPI::AttributedStringTest_Strikethrough::url):
(TestWebKitAPI::AttributedStringTest_Strikethrough::runTest):
* TestWebKitAPI/Tests/mac/attributedStringStrikethrough.html: Added.
Add tests for attributed strings with strikethrough.  Refactor the attributed string tests
to make adding more easier in the future.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153344 268f45cc-cd09-0410-ab3c-d52691b4dbfc