ScrollViewInsetTests.RestoreInitialContentOffsetAfterCrash API test is failing with...

ScrollViewInsetTests.RestoreInitialContentOffsetAfterCrash API test is failing with async delegates
https://bugs.webkit.org/show_bug.cgi?id=183787

Reviewed by Wenson Hsieh.

Source/WebCore:

* loader/FrameLoader.cpp:
(WebCore::FrameLoader::continueLoadAfterNavigationPolicy):
* loader/FrameLoaderClient.h:

Source/WebKit:

Without asynchronous policy delegates, when the client requests a navigation, we would:
1. Do a synchronous navigation policy check
2. If the client allows the navigation, start the provisional load

Starting the provisional load would freeze the layer tree until first meaningful
layout via WebFrameLoaderClient::provisionalLoadStarted() -> WebPage::didStartPageTransition().

When constructing a WebView and then requesting a load right away. This would make sure
we do not commit a layer tree for the initial about:blank page because the layer tree
would be frozen until we have something meaningful to show for the following load.

However, with asynchronous policy delegates, we are able to do a layer tree commit
during the asynchronous navigation policy check because the layer tree is not frozen
yet (provisional load has not started) and the process is not stuck on synchronous
IPC. When constructing a WebView and then requesting a load right away, this would
allow a layer tree commit for about:blank to happen before we've even started the
load. This would cause some API tests to fail on iOS.

To address the issue, we try and maintain pre-existing behavior by freezing the
layer tree during navigation policy decision.

* WebProcess/WebCoreSupport/WebFrameLoaderClient.cpp:
(WebKit::WebFrameLoaderClient::dispatchDecidePolicyForNavigationAction):
(WebKit::WebFrameLoaderClient::didDecidePolicyForNavigationAction):
* WebProcess/WebCoreSupport/WebFrameLoaderClient.h:
* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::didStartNavigationPolicyCheck):
(WebKit::WebPage::didCompleteNavigationPolicyCheck):
* WebProcess/WebPage/WebPage.h:

Tools:

Add API test coverage.

* TestWebKitAPI/Tests/ios/ScrollViewInsetTests.mm:
(-[AsyncPolicyDelegateForInsetTest webView:didFinishNavigation:]):
(-[AsyncPolicyDelegateForInsetTest webView:decidePolicyForNavigationAction:decisionHandler:]):
(-[AsyncPolicyDelegateForInsetTest webView:decidePolicyForNavigationResponse:decisionHandler:]):
(-[AsyncPolicyDelegateForInsetTest webViewWebContentProcessDidTerminate:]):
(TestWebKitAPI::TEST):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@229828 268f45cc-cd09-0410-ab3c-d52691b4dbfc