In current implementation we call PrepareForBreakPoints during getting possible breakpoints, this call produce GC and iteration through heap, but it's not needed before we set real breakpoint.

On my machine, get-possible-breakpoints-master.js without CL takes ~200ms, with CL it takes ~60 ms. Running test without getPossibleBreakpoints protocol call takes ~50 ms. It means that we have (200-50)/(60-50) = 15 times faster getPossibleBreakpoints.

R=yangguo@chromium.org,jgrubber@chromium.org

Bug: none
Change-Id: If12e41cd87dbba11a89aa5895e3b4d88123d7d3d
Reviewed-on: https://chromium-review.googlesource.com/591027
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47021}