Get rid of the "chrome" subdirectory and "metadata.common"

[sebastian]

Background

With #4577 we dropped Safari support from the master branch, removing the Safari backend (i.e. safari/ext/*) and other legacy code. However, one relic that still remains is the chrome subdirectory, which is used to separate the Chrome-specific code and assets. But since we now use these on all supported platforms, keeping them in a separate folder doesn't make any sense anymore. In particular the separation between ext/* and chrome/ext/* is holding back some further cleanup (#5084).

Also there is metadata.common, which was used to be the common baseline of Chrome and Safari, but now it merely exists so that metadata.chrome can inherit from it. These two files can be merged as well now.

What to change

Merge the contents of the chrome subdirectory into the top-level file structure. The files ext/common.js and ext/background.js will conflict, so insert the code from the respective files in the (to be removed) chrome subdirectory, at the end of the IIFE. Adjust the paths pointing to the chrome subdirectory in metadata.chrome accordingly, and finally merge metadata.common into metadata.chrome.

[abpbot]

A commit referencing this issue has landed:
​Issue 5083 - Merges chrome subdirectory into top level directory

[kzar]

As mentioned in IRC this change seems to have caused a regression relating to filter storage. I see exceptions in the background console when the extension starts and I don't have any filters or subscriptions.

adblockplus.js:820 Uncaught TypeError: Cannot read property 'get' of undefined
    at loadFile (adblockplus.js:820)
    at Object.statFile (adblockplus.js:904)
    at Object.loadFromDisk (adblockplus.js:6880)
    at init (adblockplus.js:6080)
    at Object.require.modules.filterListener (adblockplus.js:6090)
    at require (adblockplus.js:8)
    at adblockplus.js:10512
loadFile @ adblockplus.js:820
statFile @ adblockplus.js:904
loadFromDisk @ adblockplus.js:6880
init @ adblockplus.js:6080
require.modules.filterListener @ adblockplus.js:6090
require @ adblockplus.js:8
(anonymous) @ adblockplus.js:10512
messageResponder.js:80 Uncaught TypeError: ext.PageMap is not a constructor
    at messageResponder.js:80
    at messageResponder.js:431
(anonymous) @ messageResponder.js:80
(anonymous) @ messageResponder.js:431
adblockplus.js:1603 Uncaught (in promise) TypeError: Cannot read property 'get' of undefined
    at resolve (adblockplus.js:1603)
    at Promise (<anonymous>)
    at init (adblockplus.js:1601)
    at Object.require.modules.prefs (adblockplus.js:1660)
    at require (adblockplus.js:8)
    at Object.require.modules.filterStorage (adblockplus.js:6409)
    at require (adblockplus.js:8)
    at Object.require.modules.filterListener (adblockplus.js:5990)
    at require (adblockplus.js:8)
    at adblockplus.js:10512

[abpbot]

A commit referencing this issue has landed:
​Issue 5083 - Fixes backgroundScripts metadata regression from previous patch

[Ross]

Done. Does not appear to have caused any regressions (apart from the fixed one above).

ABP 1.13.2.1785
Chrome 49 / 59 / Windows 7
Opera 36 / 45 / Windows 7