Reland of Collecting encode_time_ms for each frame (patchset #1 id:1 of https://codereview.webrtc.org/1383283005/ )

Reason for revert:
The reverted commit didn't affect the tests, but the one before: https://codereview.webrtc.org/1385563005/

I've run the test that was failing (EndToEndTest.AssignsTransportSequenceNumbers) locally multiple times, and it works fine (finishes successfully in 150-170ms).

Original issue's description:
> Revert of Collecting encode_time_ms for each frame (patchset #13 id:220001 of https://codereview.webrtc.org/1374233002/ )
>
> Reason for revert:
> Breaks EndToEndTest.AssignsTransportSequenceNumbers in video_engine_tests
> on several bots:
> http://build.chromium.org/p/client.webrtc/builders/Linux64%20Debug/builds/5507
> http://build.chromium.org/p/client.webrtc/builders/Mac64%20Debug/builds/4815
> http://build.chromium.org/p/client.webrtc/builders/Win%20SyzyASan/builds/3272
> http://build.chromium.org/p/client.webrtc/builders/Linux%20Memcheck/builds/4414
>
> It seems very unfortunate that it breaks on _exactly_ the bot configs that aren't covered by the CQ trybots.
>
> Original issue's description:
> > Collecting encode_time_ms for each frame.
> >
> > Also, in Sample struct, replacing double with the original type.
> > It makes more sense to save the original data as truthful as possible, and then
> > convert it to double later if necessary (in the plot script).
> >
> > Committed: https://crrev.com/092b13384e57b33e2003d9736dfa1f491e76f938
> > Cr-Commit-Position: refs/heads/master@{#10184}
>
> TBR=sprang@webrtc.org,pbos@webrtc.org,mflodman@webrtc.org,asapersson@webrtc.org,ivica@webrtc.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
>
> Committed: https://crrev.com/810447972425e890bc7911af27f894b86e9b7e6f
> Cr-Commit-Position: refs/heads/master@{#10185}

TBR=sprang@webrtc.org,pbos@webrtc.org,mflodman@webrtc.org,asapersson@webrtc.org,kjellander@webrtc.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.webrtc.org/1390163002

Cr-Commit-Position: refs/heads/master@{#10195}
diff --git a/webrtc/video/full_stack_plot.py b/webrtc/video/full_stack_plot.py
index 0e89901..4e09b41 100755
--- a/webrtc/video/full_stack_plot.py
+++ b/webrtc/video/full_stack_plot.py
@@ -34,15 +34,16 @@
 
 # Fields
 DROPPED = 0
-INPUT_TIME = 1              # ms
-SEND_TIME = 2               # ms
-RECV_TIME = 3               # ms
-ENCODED_FRAME_SIZE = 4      # bytes
-PSNR = 5
-SSIM = 6
-RENDER_TIME = 7             # ms
+INPUT_TIME = 1              # ms (timestamp)
+SEND_TIME = 2               # ms (timestamp)
+RECV_TIME = 3               # ms (timestamp)
+RENDER_TIME = 4             # ms (timestamp)
+ENCODED_FRAME_SIZE = 5      # bytes
+PSNR = 6
+SSIM = 7
+ENCODE_TIME = 8             # ms (time interval)
 
-TOTAL_RAW_FIELDS = 8
+TOTAL_RAW_FIELDS = 9
 
 SENDER_TIME = TOTAL_RAW_FIELDS + 0
 RECEIVER_TIME = TOTAL_RAW_FIELDS + 1
@@ -66,6 +67,7 @@
     (PSNR, "psnr", "PSNR"),
     (SSIM, "ssim", "SSIM"),
     (RENDER_TIME, "render_time_ms", "render time"),
+    (ENCODE_TIME, "encode_time_ms", "encode time"),
     # Auto-generated
     (SENDER_TIME, "sender_time", "sender time"),
     (RECEIVER_TIME, "receiver_time", "receiver time"),