Fixes for allowing to run layout tests on Android again

Follow up to r167125, which broke running layout tests on Android, as
the port implementation overrides the start_http_server() implementation.

Also follows up to r167129, which removes the support for additional_dirs
from the ApacheHTTP implementation. Android uses this (together with the
forwarder) to avoid pushing all layout tests to the device, and instead
serve them from the host which is running the tests.

TBR=dpranke, scottmg

Review URL: https://codereview.chromium.org/170753002

git-svn-id: svn://svn.chromium.org/blink/trunk@167357 bbb929c8-8fbe-4397-9dbb-9b2b20218538
fix may be used uninitialized warning on older compilers

Some older compilers give a warning that m_block may be used
uninitialized, since it's not always initialised in the LayoutScope
constructor.

Review URL: https://codereview.chromium.org/170233006

git-svn-id: svn://svn.chromium.org/blink/trunk@167358 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix layering of ApplicationCacheHost

This patch moves the frame-walking code from Chromium's WebApplicationCacheHostImpl
into WebCore::ApplicationCacheHost, which breaks that class's dependency on the
public/web API.

That allows blink::WebApplicationCacheHost{,Client} to move to public/platform.
With the addition of a factory method on FrameLoaderClient, this also allos
ApplicationCacheHost.cpp to move next to its header file in core/loader/appcache.

ApplicationCacheHostInternal.h remains for now, but in the long run it can probably
be removed (though the ownership semantics aren't completely clear to me).

BUG=343272

Review URL: https://codereview.chromium.org/161213003

git-svn-id: svn://svn.chromium.org/blink/trunk@167359 bbb929c8-8fbe-4397-9dbb-9b2b20218538