Cleanup blink:: prefix usage in Source/core/modules/[mediasource/*.cpp to websockets/*.cpp]

Cleanup blink:: prefix usage in Source/core/modules/[mediasource/*.cpp to websockets/*.cpp]

- Merge multiple |namespace blink {}| blocks
- Remove unnecessary blink:: prefixes
- Make blank lines consistent

BUG=None

Review URL: https://codereview.chromium.org/469773002

git-svn-id: svn://svn.chromium.org/blink/trunk@180201 bbb929c8-8fbe-4397-9dbb-9b2b20218538