DevTools: add main side constraint on the sources panel.

BUG=342730

Review URL: https://codereview.chromium.org/159713004

git-svn-id: svn://svn.chromium.org/blink/trunk@166935 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove WTF::numberOfProcessorCores.

This has had no call sites for three months, since:
https://codereview.chromium.org/68513010

This platform-specific code doesn't belong in wtf,
especially since this is also available via the embedder as
blink::Platform::numberOfProcessors.

BUG=342786

Review URL: https://codereview.chromium.org/150243006

git-svn-id: svn://svn.chromium.org/blink/trunk@166936 bbb929c8-8fbe-4397-9dbb-9b2b20218538