Remove forward declarations from Source/core/dom/custom

This patch removes unneeded forward references and add closing comment for namespace blink

Review URL: https://codereview.chromium.org/598593006

git-svn-id: svn://svn.chromium.org/blink/trunk@182892 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Deflake serviceworkerglobalscope-scope.html by splitting it into files

The previous attempt r180710 was insufficient because
promises was misused: a().then(b()) is not the same as
a().then(function() { b(); })

This patch splits the tests into separate files so there
is no need for fragile "run all these async tests serially"
logic.

BUG=418870

Review URL: https://codereview.chromium.org/492313003

git-svn-id: svn://svn.chromium.org/blink/trunk@182893 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Credential Manager: Strict type checking for CredentialContainer::*.

BUG=418533

Review URL: https://codereview.chromium.org/612303003

git-svn-id: svn://svn.chromium.org/blink/trunk@182894 bbb929c8-8fbe-4397-9dbb-9b2b20218538