Tighten up encode time measurement in VideoProcessor.
Tighten up encode time measurement in VideoProcessor.

No point in measuring the time needed to write dropped frames to disk.

BUG=webrtc:6634

Review-Url: https://codereview.webrtc.org/2696503003
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#16629}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 32e0d26096e8bf5b2652211a464843914b7fc6db

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk