Break http/tests/xmlhttprequest/origin-exact-matching into 48 (!!!) tests.

Synchronous XMLHttpRequest is bad. 48 synchronous XMLHttpRequests in one
layout test is very bad. This test was running up to ~91 seconds on Win,
which is no fun.

Breaking it up is a bit ugly, but whatever.

Review URL: https://codereview.chromium.org/166543003

git-svn-id: svn://svn.chromium.org/blink/trunk@167274 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove CSS regions support, keeping a bare minimum to support "region-based" multicol.

Remove everything strictly specific to CSS regions, but keep the parts that
"region-based" multicol needs. So the render flow thread framework is still around,
albeit heavily trimmed down. RenderRegion has also been kept, but is now obviously
a misnomer (to be fixed later). It serves as a base class for what css3-break refers
to as a "fragmentainer" (e.g. column, page or region). Not sure if it should really
be a renderer type, seeing that these need to be created during layout (which should
be avoided for renderers). A fragmentainer is more akin to what a line box represents
than to what a renderer does.

Additional removal and cleanup is possible, but let's start with this.

BUG=none

Review URL: https://codereview.chromium.org/134473008

git-svn-id: svn://svn.chromium.org/blink/trunk@167275 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove isolatedWorldForEnteredContext() and isolatedWorldForIsolate()

- isolatedWorldForIsolate() is equivalent to DOMWrapperWorld::current()->isIsolatedWorld().

- isolatedWorldForEnteredContext() is equivalent to DOMWrapperWorld::current()->isIsolatedWorld(). Remember that the world of the current context is equal to the world of the entered context.

Thus this CL replaces these methods with DOMWrapperWorld::current()->isIsolatedWorld().

BUG=341032
R=dcarney@chromium.org, eseidel@chromium.org

Review URL: https://codereview.chromium.org/137953010

git-svn-id: svn://svn.chromium.org/blink/trunk@167276 bbb929c8-8fbe-4397-9dbb-9b2b20218538