DevTools: Slow down performance metrics chart speed.
DevTools: Slow down performance metrics chart speed.

Make the chart speed twice slower down to 10 px/sec.

Change-Id: Ifcf34ea034ac74a0fa98c5e323b7fc5fee2d3ee4
Reviewed-on: https://chromium-review.googlesource.com/c/1297985
Reviewed-by: Aleksey Kozyatinskiy <562acbea96970f508ad9f5cc9fc7c62d82dd3ef8@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <562acbea96970f508ad9f5cc9fc7c62d82dd3ef8@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#602549}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d1de8a76b5ecd425b144c9e5f922464ec69c71e6
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