commit db56a6f62c9acfc81abcdedea28fa0a6c9bb196b
author Wyatt Allen <wyatta@google.com> Mon Aug 01 15:23:50 2016 -0700
committer Wyatt Allen <wyatta@google.com> Tue Aug 02 09:51:56 2016 -0700
tree 0e3abe18f4f8ca37edfb035be45496e370907b1e
parent f1063a2690683231e1935b47a64dfde7857a8fe6

Lazy load HighlightJS library

Previously, the HighlightJS library (HLJS) was being Vulcanized into the
PolyGerrit build, even if the library was not being used (for example if
the user does not navigate to a diff or has syntax highlighting disabled
in preferences). Because HLJS is a substantial file -- ranging in size
from 47KB to more than 455KB (ungizpped) depending on the build
environment, this is not ideal.

In order to lazy load a JS library:

1)  It needs to be copied into the built WAR file to be addressable, and
2)  It should not be Vulcanized into the built gr-app.js file.

Previously, the PolyGerrit build system supported copying and
non-vulcanizing exactly one JS library: namely webcomponents-lite.js.
This change generalizes the mechanism by which webcomponents is copied
and adds HLJS to that list. This satisfies **1**.

Furthermore, the GR-SYNTAX-LAYER is rewritten to dynamically import HLJS
in the `process` step by crafting a SCRIPT element and attaching it to
the local DOM. (Syntax processing is invoked only after entire diff is
rendered.) Code that depends on the library awaits this load before
using it. Thus, the conventional JS import can be removed from the
element's HTML and will not be recognized by the Vulcanize phase. This
satisfies **2**.

Tests are updated accordingly.

Bug: Issue 4298
Change-Id: I9a95d6d4c211cd8f1ca1bc4daec770b64b22b3d1