M38 gardening: update signatures in XWalkMediaCaptureDevicesDispatcher.

CL: https://codereview.chromium.org/364123002
M38 gardening: AppCacheService is in content now.

CL: https://codereview.chromium.org/344493002
M38 gardening: Update HandleExternalProtocol's signature.

CL: https://codereview.chromium.org/426713002
M38 gardening: adapt to ResourceType's changes.

CL: https://codereview.chromium.org/425653002
M38 gardening: ServerBoundCert is now ChannelID.

CL: https://codereview.chromium.org/356713005
M38 gardening: Remove reference to switches::kEnableGestureTapHighlight.

It is now always enabled unconditionally.

CL: https://codereview.chromium.org/393653002
M38 gardening: conditionally include nacl_process_host.h.

CL: https://codereview.chromium.org/421613002
M38 gardening: Changes to WebNotification-related signatures.

CL: https://codereview.chromium.org/405633002
M38 gardening: drop NaCl dependencies when it is disabled.

CL: https://codereview.chromium.org/321423002
M38 gardening: Add missing method to RuntimeContext.

CL: https://codereview.chromium.org/369703002