improve logEntry hit testing performance
fixing flame graph rendering
adding some comments
adding flamechart highlighting

Bug: v8:10644, v8:11835
Change-Id: I2ab2f63b9e8339c6c25bb7023772fc97dfc56c2e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2959615
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75130}