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Currently we use a dynamically created trace event name this has a
couple implications:

1) Has to be computed at run time and allocated dynamically, and copied
   by the TraceEvent implementation.
2) Will be stripped from traces when tracing with privacy filtering
   enabled.
3) Has to be serialized and sent over mojo and then parsed.

This fixes all of these by directly computing the trace name as a
static string. This comes potentially at the slight cost of binary size
(since now the strings need to be stored in the full form), but this is
limited to ("InputLatency::" + Name(num WebInputEvent::Type)) * number of
Types, and we get to remove some mojo code so it should end up close to a
wash in binary size (+528 bytes).

Change-Id: I285d8bb24f8497bc067480201fdd3bac0b390083
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062286Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Auto-Submit: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742963}