Add Tracing.getCategories to protocol.json.

BUG=

Review URL: https://codereview.chromium.org/331303002

git-svn-id: svn://svn.chromium.org/blink/trunk@176439 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Qualify RuntimeEnabledFeatures.h and remove unnecessary include dir.

This CL removes the gen/blink/platform dir in core.gyp and qualifies
all the instances that include RuntimeEnabledFeatures.h.

BUG=381876

Review URL: https://codereview.chromium.org/344593002

git-svn-id: svn://svn.chromium.org/blink/trunk@176440 bbb929c8-8fbe-4397-9dbb-9b2b20218538