Oilpan: Web SQL: Fix an assertion failure in ~DatabaseCloser.

Use closeDatabase() instead of closeImmediately().
We had the following assertion failure in Oilpan:

ASSERTION FAILED: state->isAllocationAllowed()
../../third_party/WebKit/Source/platform/heap/Heap.h(1459) : static Address blink::Heap::allocate(size_t) [T = blink::ConsoleMessage]
1   0x7535136 unsigned char* blink::Heap::allocate<blink::ConsoleMessage>(unsigned long)
2   0x753508b blink::GarbageCollected<blink::ConsoleMessage>::operator new(unsigned long)
3   0x75230f4 blink::ConsoleMessage::create(blink::MessageSource, blink::MessageLevel, WTF::String const&, WTF::String const&, unsigned int, unsigned int)
4   0x7fc0f78 blink::DatabaseBackendBase::logErrorMessage(WTF::String const&)
5   0x7fdf531 blink::DatabaseSync::closeImmediately()
6   0x7fd044d blink::DatabaseContext::DatabaseCloser::~DatabaseCloser()

because the code tried to allocate ConsoleMessage during Oilpan weak processing.

We should not use closeImmediately().
- DatabaseCloser used it just because closeDatabase() was not public.
- closeImmediately() shows a console message. This behavior is not compatible
  with non-Oilpan build.

BUG=347902

Review URL: https://codereview.chromium.org/465223004

git-svn-id: svn://svn.chromium.org/blink/trunk@180546 bbb929c8-8fbe-4397-9dbb-9b2b20218538