Merge 123495 - Files from drag and file <input> should use getMIMETypeForExtension to determine con…

Merge 123495 - Files from drag and file <input> should use getMIMETypeForExtension to determine content type.
https://bugs.webkit.org/show_bug.cgi?id=91702

Reviewed by Jian Li.

Awhile back, we changed File to only use getWellKnownMIMETypeForExtension to prevent web
pages from being able to detect what applications a user has installed indirectly through
the MIME types. However, some sites like YouTube's drag and drop uploader use MIME types
that aren't in WebKit's internal list, so we relax the restriction for Files that originate
from an user action.

* fileapi/File.cpp:
(WebCore::getContentTypeFromFileName):
(WebCore::createBlobDataForFile):
(WebCore::createBlobDataForFileWithName):
(WebCore::createBlobDataForFileWithMetadata):
(WebCore::File::createWithRelativePath):
(WebCore::File::File):
* fileapi/File.h:
(File):
(WebCore::File::create):
(WebCore::File::createWithName):
* html/FileInputType.cpp:
(WebCore::FileInputType::createFileList):
* platform/chromium/ChromiumDataObject.cpp:
(WebCore::ChromiumDataObject::addFilename):
* platform/gtk/ClipboardGtk.cpp:
(WebCore::ClipboardGtk::files):
* platform/mac/ClipboardMac.mm:
(WebCore::ClipboardMac::files):
* platform/qt/ClipboardQt.cpp:
(WebCore::ClipboardQt::files):
* platform/win/ClipboardWin.cpp:
(WebCore::ClipboardWin::files):

TBR=dcheng@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=123677