[Android] Add gn support for multidex.

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index 9e4270d26009f853e37dc7af883bed4cb43705c8..752ccf6b7e77052da1b0680237d239d7a5eb6920 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -1731,6 +1731,9 @@ if (is_android) {
     sources = [
       "android/java/templates/ChromiumMultiDex.template",
     ]
+    if (is_debug) {
+      defines = [ "CONFIGURATION_NAME_Debug" ]
+    }

[Nico, 2015/11/16 21:46:54]

why isn't this needed for gyp?

[jbudorick, 2015/11/16 21:49:18]

it is, though it's handled a little differently there because we can't switch on
build type in gyp:

https://codereview.chromium.org/1408163009/diff/110001/base/base.gyp line 1473

[Nico, 2015/11/16 21:57:55]

Ah, ok. (You can switch on build type in gyp if you want as far as I know, e.g.:
https://code.google.com/p/chromium/codesearch#chromium/src/breakpad/breakpad....)

Why is this needed only for base? (I tried to find ChromiumMultiDex.template,
but cs.chromium.org doesn't seem to know about it. There's a
ChromiumMultiDex.java but it doesn't use anything that looks like
CONFIGURATION_NAME_). This path points to
https://code.google.com/p/chromium/codesearch#chromium/src/base/android/java/...
which doesn't contain the .template file – maybe you forgot to git add it at
some point in the past?

[jbudorick, 2015/11/16 22:00:21]

Maybe code search had a bad weekend? It's in there:
https://codereview.chromium.org/1408163009/diff/110001/base/android/java/temp...

[Nico, 2015/11/16 22:04:51]

Oh, it's even in this CL, cool, thanks.

…why does the behavior of install() change with build type? Why does
processIsIsolated() only exist in debug builds?

Problems I have with this:

1. CONFIGURATION_NAME_Debug looks like an overly broad name. People might
copy-paste that into their .templates, yet this is only defined correctly for
the base target.

2. Having big behavior differences like this between Release and Debug is
probably not a good idea. For example, the trybots don't run tests in debug but
in release with dchecks enabled – so this should probably be keyed off the "are
dchecks on?" define instead if it needs to be conditional.

[jbudorick, 2015/11/16 22:19:33]

er... it was in the last one.
because we don't currently want to do multidex installation at all in release
builds. Even with a single dex, it caused a pretty big start-up regression:
https://code.google.com/p/chromium/issues/detail?id=525695

It's only necessary in debug builds because we run proguard in release builds,
which puts us comfortably below the dex limit.

[jbudorick, 2015/11/17 16:27:06]

made this define clearly multidex-specific.

[jbudorick, 2015/11/17 16:27:06]

(code search did have a bad weekend:
https://build.chromium.org/p/chromium.infra.cron/builders/Chromium%20Linux%20...)

[jbudorick, 2015/11/17 16:27:06]

also, I tried these when I was writing the gyp patch but couldn't get it to work
for targets that aren't doing c++ compilation (like this one).

     package_name = "org/chromium/base/multidex"
   }