Remove some tracing methods from blink::Platform

Now we can directly use trace_event macros to implement EventTracer. Remove
unnecessary indirections. This is also a preparation to add
EstimateTraceMemoryOverhead() to blink's TracedValue.

BUG=561879, 570961

Review URL: https://codereview.chromium.org/1544123002

Cr-Commit-Position: refs/heads/master@{#370066}
15 files changed