[iOS] Multiple links in Mail are dropped in a single line, and are difficult to tell...

[iOS] Multiple links in Mail are dropped in a single line, and are difficult to tell apart
https://bugs.webkit.org/show_bug.cgi?id=185289
<rdar://problem/35756912>

Reviewed by Tim Horton and Darin Adler.

Source/WebCore:

When inserting multiple URLs as individual items in a single drop, we currently separate each item with a space
(see r217284). However, it still seems difficult to tell dropped links apart. This patch makes some slight
tweaks to WebContentReader::readURL so that it inserts line breaks before dropped URLs, if the dropped URL isn't
the first item to be inserted in the resulting document fragment.

Augments existing API tests in DataInteractionTests.

* editing/ios/WebContentReaderIOS.mm:

Additionally remove some extraneous header imports from this implementation file.

(WebCore::WebContentReader::readURL):

Tools:

Augment and rebaseline some iOS drag-and-drop API tests that handle dropping URLs as a part of multi-item drop
sessions.

* TestWebKitAPI/Tests/ios/DataInteractionTests.mm:
(TestWebKitAPI::TEST):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@231396 268f45cc-cd09-0410-ab3c-d52691b4dbfc