core: replace WebInspector traceparser with native JSON.parse

[brendankenny]

possibly more controversial than #6090 and #6091

The reason we introduced a streaming trace parser was because we would get RangeError: Invalid string length with traces that were larger than 256MB, the previous maximum string size in V8.

This changed in V8 6.2, which increased the max size to 1GB. This landed in Node 8.10.0 in March, which is after the original LTS release of 8.9. However:

• the LTS branch expects users to keep up with MINOR updates. 8.9.4 was the last release in the 8.9.x branch in January, and major security updates have happened in 8.11.0, 8.11.3, 8.11.4
• trace parser is now only used for -A mode after core(driver): deliver trace as events rather than a stream #6056
• since 3.0, our traces have been significantly smaller (e.g. a full time-out verge run is more like 150MB)

It thus seems reasonable to expect at least Node 8.10 to run Lighthouse if we're supporting at least the LTS branch. I've updated the package.json engines entry to give a warning on install in npm (not sure what the yarn engines behavior is these days).

[brendankenny]

Before this PR, lighthouse-ext-background.js was pulling in assetSaver, which was pulling in WebInspector, which was setting global.window = global, so this file was fine to pull into node unit tests.

With that dependency path removed, this protects us from erroring on the window access (in the actual extension the behavior is unchanged since window is already defined :)

[brendankenny]

removes another 6KB off our gzipped bundle (508.62KB -> 502.56KB) since we can remove some of the other common/ and sdk/ files in addition to the parser itself.

[brendankenny]

oh and

• it's faster to just JSON.parse the string. Loading artifacts with that 150MB trace takes about 2760ms on master for me, 1618ms after this PR

[paulirish]

i'm good with the compat implications. all non-node clients are good already. only affects Node <8.10 and only in -A. -G and --save-assets are still good as they use the streaming trace-saver.

[patrickhulce]

heh, I was going to suggest this too :D nice!!!