Introduce the chroot_cmd flag that contains the command line prefix for...

Introduce the chroot_cmd flag that contains the command line prefix for running in a chrooted environment.

Right now when supplying a 32-bit sysroot via the 'sysroot' GYP flag on a 64-bit host arch,
pkg-config (and pkg-config-wrapper) fail to generate the correct 32-bit paths within that sysroot.
The solution is to chroot into that directory and run pkg-config from there.
This is intended to work with schroot scripts like 'precise32' generated when running build/install-chroot.sh

BUG=324207
R=piman@chromium.org

Review URL: https://codereview.chromium.org/163583003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251353 0039d316-1c4b-4281-b951-d872f2087c98

build/common.gypi

@@ -287,6 +287,7 @@
 
       # The system root for cross-compiles. Default: none.
       'sysroot%': '',
+      'chroot_cmd%': '',
 
       # The system libdir used for this ABI.
       'system_libdir%': 'lib',
@@ -913,6 +914,7 @@
     'arm_neon%': '<(arm_neon)',
     'arm_neon_optional%': '<(arm_neon_optional)',
     'sysroot%': '<(sysroot)',
+    'chroot_cmd%': '<(chroot_cmd)',
     'system_libdir%': '<(system_libdir)',
     'component%': '<(component)',
     'use_titlecase_in_grd_files%': '<(use_titlecase_in_grd_files)',

build/linux/system.gyp

@@ -6,7 +6,7 @@
   'variables': {
     'conditions': [
       ['sysroot!=""', {
-        'pkg-config': './pkg-config-wrapper "<(sysroot)" "<(target_arch)"',
+        'pkg-config': '<(chroot_cmd) ./pkg-config-wrapper "<(sysroot)" "<(target_arch)"',
       }, {
         'pkg-config': 'pkg-config'
       }],