MD History: Run polymer-css-build over vulcanized output

polymer-css-build preprocesses CSS to perform transformations
ahead-of-time that would otherwise need to be done by the browser during
page load. This saves approximately 5% off page load for MD History, and
should have a similar impact on MD Downloads.

BUG=629406,629710
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2268863002
Cr-Commit-Position: refs/heads/master@{#416496}

chrome/browser/resources/vulcanize.py

@@ -92,6 +92,7 @@ def _vulcanize(directory, host, html_in_file, html_out_file='vulcanized.html',
                          '--beautify', 'indent-level=2,quote_style=3',
                          '--comments', '/Copyright|license|LICENSE|\<\/?if/',
                          '--output', js_out_path])
+    _run_cmd(['polymer-css-build', html_out_path])
   finally:
     os.remove(tmp.name)
 

docs/vulcanize.md

@@ -13,6 +13,7 @@ Vulcanization currently requires:
 - vulcanize: 1.14.8 (can be found with `vulcanize --version`)
 - crisper: 2.0.1 (can be found with `npm list -g crisper`)
 - uglifyjs: 2.4.10 (can be found with `uglifyjs --version`)
+- polymer-css-build: 0.0.6 (can be found with `npm list -g polymer-css-build`)
 
 ## Installing required software
 
@@ -28,11 +29,11 @@ $ npm config set -g prefix "$HOME/node_modules"
 Then install the required modules:
 
 ```bash
-$ npm install -g crisper vulcanize
+$ npm install -g crisper vulcanize uglifyjs polymer-css-build
 ```
 
-Ultimately, all that is required to run this script is that `crisper`, 'uglify'
-and `vulcanize` are on your `$PATH`.
+Ultimately, all that is required to run this script is that the node binaries
+listed above are on your $PATH.
 
 ## Combining resources with vulcanize