chromium: Update beta and dev channels to latest.

This updates the channels to the following new versions:

beta: 27.0.1453.47 -> 27.0.1453.65 (builds fine, tested)
dev:  27.0.1453.47 -> 28.0.1485.0  (builds fine, tested)

As we now don't have any version below 26, this update drops all references to
all older versions as well.

In addition to that, the /usr/bin/gcc reference from:

third_party/WebKit/Source/core/core.gyp/core.gyp

Can now - starting at version 28 - be found in:

third_party/WebKit/Source/WebCore/WebCore.gyp/WebCore.gyp

Signed-off-by: aszlig <aszlig@redmoonstudios.org>