Access environment variables through Host object instead of directly.

third_party/WebKit/Tools/Scripts/webkitpy/common/system/systemhost_mock.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/common/system/systemhost_mock.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/common/system/systemhost_mock.py b/third_party/WebKit/Tools/Scripts/webkitpy/common/system/systemhost_mock.py
index d309d47fd7b2b249159657fa7f7d2f468bf51726..76d19b7274e2dd907aad563850f3d1635b88db61 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/common/system/systemhost_mock.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/common/system/systemhost_mock.py
@@ -28,7 +28,6 @@
 
 from StringIO import StringIO
 
-from webkitpy.common.system.environment import Environment
 from webkitpy.common.system.executive_mock import MockExecutive
 from webkitpy.common.system.filesystem_mock import MockFileSystem
 from webkitpy.common.system.platforminfo_mock import MockPlatformInfo
@@ -56,9 +55,19 @@ class MockSystemHost(object):
         self.stdin = StringIO()
         self.stdout = StringIO()
         self.stderr = StringIO()
+        self._env = {
+            'MOCK_ENVIRON_COPY': '1',
+            'PATH': '/bin:/mock/bin'
+        }
 
     def copy_current_environment(self):
-        return Environment({"MOCK_ENVIRON_COPY": '1'})
+        return self._env.copy()
+
+    def get_env(self, key, default=None):
+        return self._env.get(key, default)
+
+    def set_env(self, key, value):
+        self._env[key] = value
 
     def print_(self, *args, **kwargs):
         sep = kwargs.get('sep', ' ')