[iOS] Use PDFKit to render PDFs in WKWebView

[iOS] Use PDFKit to render PDFs in WKWebView
https://bugs.webkit.org/show_bug.cgi?id=184387

Reviewed by Beth Dakin.

Source/WebKit:

Adopted PDFHostViewController for rendering PDFs in WKWebView.

This patch implements rendering the PDF document and page number indicator. Link
navigation, find-in-page, and printing will be implemented in follow-up patches.

WKLegacyPDFView is still the default PDF view.

* Configurations/WebKit.xcconfig:

Linked WebKit with PDFKit on iOS.

* UIProcess/API/Cocoa/WKWebView.mm:
(-[WKWebView _currentContentView]):
(-[WKWebView viewForZoomingInScrollView:]):

When WKPDFView loads a PDF document, it replaces itself with a view vended by
PDFHostViewController as the WKScrollView's content view. Abstracted WKWebView's
concept of the "current content view" to be either the WKContentView or a view of
the custom content view's choosing (-web_contentView).

(-[WKWebView scrollViewWillBeginZooming:withView:]):
(-[WKWebView scrollViewDidZoom:]):
(-[WKWebView scrollViewDidEndZooming:withView:atScale:]):

Forwarded these calls to _customContentView if it responds to the equivalent
WKWebViewContentProvider selectors.

* UIProcess/Cocoa/WKWebViewContentProvider.h:

Defined new protocol selectors.

* UIProcess/Cocoa/WKWebViewContentProviderRegistry.mm:
(-[WKWebViewContentProviderRegistry init]):
* UIProcess/ios/WKLegacyPDFView.h:
* UIProcess/ios/WKLegacyPDFView.mm:

Changed ENABLE(WKPDFVIEW) to ENABLE(WKLEGACYPDFVIEW).

(-[WKLegacyPDFView web_contentView]):

Added. Returns self as the content view.

* UIProcess/ios/WKPDFView.h: Added.
* UIProcess/ios/WKPDFView.mm: Added.
(-[WKPDFView dealloc]):

Removed the host view and page number indicator from their superviews.

(-[WKPDFView gestureRecognizerShouldBegin:]):

Forwarded to _hostViewController.

(-[WKPDFView web_initWithFrame:webView:]):

Set ours and the scroll view's background color to UIColor.grayColor to match
WKLegacyPDFView.

(-[WKPDFView web_setContentProviderData:suggestedFilename:]):

Created a PDFHostViewController and set its root view as the scroll view's content
view after removing the WKPDFView itself. This allows WKPDFView to act as a
placeholder content view until the PDF is loaded. Added the host view controller's
page number indicator to the fixed overlay view. Finally, loaded the PDF document
by calling -[PDFHostViewController setDocumentData:withScrollView:].

(-[WKPDFView _offsetForPageNumberIndicator]):

Computed an offset for the page number indicator like WKLegacyPDFView did, taking
into account the overlaid accessory views inset, computed unobscured safe area
inset, and computed obscured inset.

(-[WKPDFView _movePageNumberIndicatorToPoint:animated:]):

Moved the page number indicator using the margin and animation duration from
WKLegacyPDFView.

(-[WKPDFView _updateLayoutAnimated:]):

Added a convenience method to update the PDF view layout and position the page
number indicator.

(-[WKPDFView web_setMinimumSize:]):

Updated our own frame in case we are still the placeholder content view.
Called -_updateLayoutAnimated:.

(-[WKPDFView web_setOverlaidAccessoryViewsInset:]):

Stored the inset and called -_updateLayoutAnimated:.

(-[WKPDFView web_computedContentInsetDidChange]):

Called -_updateLayoutAnimated:.

(-[WKPDFView web_setFixedOverlayView:]):

Stored the fixed overlay view.

(-[WKPDFView web_didSameDocumentNavigation:]):
(-[WKPDFView web_countStringMatches:options:maxCount:]):
(-[WKPDFView web_findString:options:maxCount:]):
(-[WKPDFView web_hideFindUI]):

Added FIXMEs.

(-[WKPDFView web_contentView]):

If there is a host view controller, return its root view. Otherwise, return self.

(-[WKPDFView web_scrollViewDidScroll:]):
(-[WKPDFView web_scrollViewWillBeginZooming:withView:]):
(-[WKPDFView web_scrollViewDidEndZooming:withView:atScale:]):
(-[WKPDFView web_scrollViewDidZoom:]):

Called -[PDFHostViewController updatePDFViewLayout].

(-[WKPDFView web_dataRepresentation]):

Returned _data.

(-[WKPDFView web_suggestedFilename]):

Returned _suggestedFilename.

(-[WKPDFView web_isBackground]):

Returned self.isBackground.

* UIProcess/ios/WKSystemPreviewView.mm:
(-[WKSystemPreviewView web_contentView]):

Added. Returns self as the content view.

* WebKit.xcodeproj/project.pbxproj:

Source/WTF:

* wtf/FeatureDefines.h: Defined ENABLE_WKLEGACYPDFVIEW and ENABLE_WKPDFVIEW.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@230487 268f45cc-cd09-0410-ab3c-d52691b4dbfc