9 files changed, 42 insertions, 40 deletions
diff --git a/third_party/bzip2/bzip2.scons b/third_party/bzip2/bzip2.scons
index f1ad082..6089ea1 100644
--- a/third_party/bzip2/bzip2.scons
+++ b/third_party/bzip2/bzip2.scons
@@ -8,8 +8,17 @@ Configuration for building bzip2.lib / libbzip2.a.
 
 Import('env')
 
+if env.WantSystemLib('bzip2'):
+  Return()
+
 env = env.Clone()
 
+env.Append(
+    CPPDEFINES = [
+        'BZ_NO_STDIO',
+    ],
+)
+
 if env['PLATFORM'] == 'win32':
   env.Append(
       CCFLAGS = [
@@ -19,12 +28,6 @@ if env['PLATFORM'] == 'win32':
       ],
   )
 
-env.Append(
-    CPPDEFINES = [
-        'BZ_NO_STDIO',
-    ],
-)
-
 input_files = [
     'blocksort.c',
     'bzlib.c',
diff --git a/third_party/bzip2/using_bzip2.scons b/third_party/bzip2/using_bzip2.scons
index b41bca2..cbe837c 100644
--- a/third_party/bzip2/using_bzip2.scons
+++ b/third_party/bzip2/using_bzip2.scons
@@ -8,8 +8,7 @@ Settings for other components using the bzip2 library.
 
 Import("env")
 
-env.Append(
-    LIBS = [
-        env['BZIP2_LIB'],
-    ],
-)
+if env.WantSystemLib('bzip2'):
+    env.Append(LIBS = ['bz2'])
+else:
+    env.Append(LIBS = ['bzip2'])
diff --git a/third_party/libjpeg/SConscript b/third_party/libjpeg/libjpeg.scons
index 381d437..fdb2c2a 100644
--- a/third_party/libjpeg/SConscript
+++ b/third_party/libjpeg/libjpeg.scons
@@ -32,6 +32,9 @@ Import('env')
 
 env = env.Clone()
 
+if env.WantSystemLib('libjpeg'):
+  Return()
+
 env.Prepend(
     CPPPATH = [
         '$CHROME_SRC_DIR',
diff --git a/third_party/libpng/libpng.scons b/third_party/libpng/libpng.scons
index 0f8bd89..01a932d 100644
--- a/third_party/libpng/libpng.scons
+++ b/third_party/libpng/libpng.scons
@@ -9,11 +9,14 @@ Configuration for building libpng.lib / libpng.a.
 
 Import('env')
 
+if env.WantSystemLib('libpng'):
+  Return()
+
 env = env.Clone()
 
-env.SConscript([
+env.ApplySConscript([
     '$ZLIB_DIR/using_zlib.scons',
-], {'env':env})
+])
 
 env.Prepend(
     CPPPATH = [
diff --git a/third_party/libxml/SConscript b/third_party/libxml/libxml.scons
index f952a96..d403cd4 100644
--- a/third_party/libxml/SConscript
+++ b/third_party/libxml/libxml.scons
@@ -29,6 +29,9 @@
 
 Import('env')
 
+if env.WantSystemLib('libxml'):
+  Return()
+
 env = env.Clone()
 
 env.Prepend(
@@ -40,9 +43,6 @@ env.Prepend(
         'DerivedSources/include',
         'include',
     ],
-)
-
-env.Append(
     CPPDEFINES = [
         'U_STATIC_IMPLEMENTATION',
         'LIBXML_STATIC',
diff --git a/third_party/libxml/using_libxml.scons b/third_party/libxml/using_libxml.scons
index 4a5c1329..709520f 100644
--- a/third_party/libxml/using_libxml.scons
+++ b/third_party/libxml/using_libxml.scons
@@ -8,27 +8,10 @@ Settings for other components using the libxml library.
 
 Import("env")
 
-env.Append(
-    CPPPATH = [
-        '$LIBXML_DIR/include',
-        '$LIBXML_DIR/DerivedSources/include',
-    ],
-    CPPDEFINES = [
-        'LIBXML_STATIC',
-    ],
-    LIBS = [
-        env['XML_LIB'],
-    ],
-)
-# Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-__doc__ = """
-Settings for other components using the libxml library.
-"""
-
-Import("env")
+if env.WantSystemLib('libxml'):
+  env.Append(LIBS = ['xml2'])
+else:
+  env.Append(LIBS = ['libxml'])
 
 env.Append(
     CPPPATH = [
@@ -38,7 +21,4 @@ env.Append(
     CPPDEFINES = [
         'LIBXML_STATIC',
     ],
-    LIBS = [
-        env['XML_LIB'],
-    ],
 )
diff --git a/third_party/libxslt/SConscript b/third_party/libxslt/libxslt.scons
index d28fb75..9a9ff71 100644
--- a/third_party/libxslt/SConscript
+++ b/third_party/libxslt/libxslt.scons
@@ -31,6 +31,9 @@ Import('env')
 
 env = env.Clone()
 
+if env.WantSystemLib('libxslt'):
+  Return()
+
 env.Prepend(
     CPPPATH = [
         '$LIBXML_DIR/DerivedSources/include',
diff --git a/third_party/lzma_sdk/lzma_sdk.scons b/third_party/lzma_sdk/lzma_sdk.scons
index b76a2d22..86ea6aa 100644
--- a/third_party/lzma_sdk/lzma_sdk.scons
+++ b/third_party/lzma_sdk/lzma_sdk.scons
@@ -6,6 +6,9 @@ Import('env')
 
 env = env.Clone()
 
+if env.WantSystemLib('lzma_sdk'):
+  Return()
+
 env.Prepend(
     CPPPATH = [
         '.',
diff --git a/third_party/zlib/zlib.scons b/third_party/zlib/zlib.scons
index a7dcb89..d37fafa 100644
--- a/third_party/zlib/zlib.scons
+++ b/third_party/zlib/zlib.scons
@@ -8,8 +8,16 @@ Configuration for building zlib.lib / libzlib.a.
 
 Import('env')
 
+if env.WantSystemLib('zlib'):
+  env.Append(ZLIB_LIB = ['z'])
+  Return()
+
 env = env.Clone()
 
+env.Append(
+    ZLIB_LIB = ['zlib'],
+)
+
 if env['PLATFORM'] == 'win32':
   env.Append(
       CCFLAGS = [