This should speed up trace generation for cpu profile as it eliminates
creation of temporary std::string objects.

Review-Url: https://codereview.chromium.org/2555043003
Cr-Commit-Position: refs/heads/master@{#41736}

JavaScript cannot represent integer larger than 2^53 - 1 from JSON, thus this
patch removes AppendLongInteger and convert long integer to string using
std::to_string.

TBR=cbruni@chromium.org

Review-Url: https://codereview.chromium.org/2557463003
Cr-Commit-Position: refs/heads/master@{#41533}

We introduced TracedValue into V8 tracing previously, this patch uses it to
build JSON string of runtime statistics instead of using stringstream as buffer.

BUG=v8:5089
LOG=N

Review-Url: https://chromiumcodereview.appspot.com/2418303002
Cr-Commit-Position: refs/heads/master@{#40443}

BUG=chromium:406277

Review-Url: https://codereview.chromium.org/2399463004
Cr-Commit-Position: refs/heads/master@{#40049}