https://bugs.webkit.org/show_bug.cgi?id=111883

Reviewed by Anders Carlsson.

This allows for properly keeping extensions in NetworkBlobRegistry for as long as
they are needed.

The patch also fixes a bug where extensions would leak when navigating between
file:// pages.

* NetworkProcess/SchedulableLoader.cpp:
Revoke the extensions, but don't invalidate - we may need them later.

* Shared/Downloads/Download.cpp:
(WebKit::Download::didFinish):
(WebKit::Download::didFail):
(WebKit::Download::didCancel):
Replaced invalidate() with revoke() and clearing out. SandboxExtension destructor
now requires revocations wto be balanced, as otherwise understanding dual reference
counting in SandboxExtension would be too difficult.

* Shared/SandboxExtension.h: We now keep track of how many times the extension
was consumed. Eventually, we should refactor the class to not have such duplicate
reference counting.
* Shared/mac/SandboxExtensionMac.mm:
(WebKit::SandboxExtension::SandboxExtension): Initialize use count.
(WebKit::SandboxExtension::~SandboxExtension): We now require consume/revoke calls
to be balanced. This is not hard to do in existing usage, and makes the design much
more reliable.
(WebKit::SandboxExtension::revoke): Don't permanently destroy the extension when
invalidatid, we may need it in the future.
(WebKit::SandboxExtension::consume): Added use counting.

* Shared/WebMemorySampler.cpp: (WebKit::WebMemorySampler::stop): This extension
is not going to be reused.

* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::performDragControllerAction): Pending extensions are not consumed,
so there is no need to revoke.
(WebKit::WebPage::SandboxExtensionTracker::invalidate): Pending extension is not
consumed, and the other two always are.
(WebKit::WebPage::SandboxExtensionTracker::setPendingProvisionalSandboxExtension):
Pending extension is never consumed in place, no need to revoke.
(WebKit::WebPage::SandboxExtensionTracker::didStartProvisionalLoad): Do not unset
reused committed extension yet - we may need it later if provisional load fails.
Thanks to use counting, we can now consume the same extension as both committed
and provisional.
(WebKit::WebPage::SandboxExtensionTracker::didCommitProvisionalLoad): Now the
committed extension can be revoked and replaced.
(WebKit::WebPage::SandboxExtensionTracker::didFailProvisionalLoad): Just revoke
provisional extension, committed one is still in place.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145369 268f45cc-cd09-0410-ab3c-d52691b4dbfc