MD Downloads: add a use_vulcanize option to Chrome

use_vulcanize is on by default. This means that release, official,
and debug builds that don't need debug versions of webui pages will
get the fastest experience.

To turn off vulcanization for local development, set

  use_vulcanize=0

in GYP, or

  use_vulcanize = false

in GN.

To conditionally include files in .grd files, do:

  <if expr="use_vulcanize">

and in C++:

  #include "chrome/common/features.h"
  #if BUILDFLAG(USE_VULCANIZE)

Currently, only the new Material Design downloads page is vulcanized,
but there will soon be others.

R=groby@chromium.org,thakis@chromium.org
BUG=541455
TEST=smaller binary

Review URL: https://codereview.chromium.org/1494253003

Cr-Commit-Position: refs/heads/master@{#367226}

1 files changed, 6 insertions, 0 deletions

diff --git a/chrome/chrome_features.gypi b/chrome/chrome_features.gypi
index 06488b1..1042f41 100644
--- a/chrome/chrome_features.gypi
+++ b/chrome/chrome_features.gypi
@@ -21,17 +21,23 @@
           'enable_google_now%': 1,
         }]
       ],
+
+      # Use vulcanized HTML/CSS/JS resources to speed up WebUI (chrome://)
+      # pages. https://github.com/polymer/vulcanize
+      'use_vulcanize%': 1,
     },
 
     # Anything in the conditions needs to be copied to the outer scope to be
     # accessible.
     'enable_google_now%': '<(enable_google_now)',
     'android_java_ui%': '<(android_java_ui)',
+    'use_vulcanize%': '<(use_vulcanize)',
 
     # Grit defines based on the feature flags. These must be manually added to
     # grit targets.
     'chrome_grit_defines': [
       '-D', 'enable_google_now=<(enable_google_now)',
+      '-D', 'use_vulcanize=<(use_vulcanize)',
     ]
   },
 }