[cr tool] Adding the concept of a target platform.

tools/cr/cr/base/platform.py

Index: tools/cr/cr/base/platform.py
diff --git a/tools/cr/cr/base/platform.py b/tools/cr/cr/base/platform.py
new file mode 100644
index 0000000000000000000000000000000000000000..7155d2bc7102526f27a7c143ce10b6e92df3daff
--- /dev/null
+++ b/tools/cr/cr/base/platform.py
@@ -0,0 +1,70 @@
+# Copyright (c) 2013 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.
+
+"""Module for the target platform support."""
+
+from importlib import import_module
+import os
+
+import cr
+
+DEFAULT = cr.Config.From(
+    DEPOT_TOOLS=os.path.join('{GOOGLE_CODE}', 'depot_tools'),
+)
+
+
+class Platform(cr.Plugin, cr.Plugin.Type):
+  """Base class for implementing cr platforms.
+
+  A platform is the target operating system being compiled for (linux android).
+  """
+
+  _platform_module = import_module('platform', None)
+  SELECTOR = 'CR_PLATFORM'
+
+  @classmethod
+  def AddArguments(cls, parser):
+    parser.add_argument(
+        '--platform', dest=cls.SELECTOR,
+        choices=cls.Choices(),
+        default=None,
+        help='Sets the target platform to use. Overrides ' + cls.SELECTOR
+    )
+
+  @classmethod
+  def System(cls):
+    return cls._platform_module.system()
+
+  def __init__(self):
+    super(Platform, self).__init__()
+
+  def Activate(self, context):
+    super(Platform, self).Activate(context)
+    if _PathFixup not in context.fixup_hooks:
+      context.fixup_hooks.append(_PathFixup)
+
+  @cr.Plugin.activemethod
+  def Prepare(self, context):
+    pass
+
+  @property
+  def paths(self):
+    return []
+
+
+def _PathFixup(context, key, value):
+  """A context fixup that does platform specific modifications to the PATH."""
+  if key == 'PATH':
+    paths = []
+    for entry in Platform.GetActivePlugin(context).paths:
+      entry = context.Substitute(entry)
+      if entry not in paths:
+        paths.append(entry)
+    for entry in value.split(os.path.pathsep):
+      if entry.endswith(os.path.sep + 'goma'):
+        pass
+      elif entry not in paths:
+        paths.append(entry)
+    value = os.path.pathsep.join(paths)
+  return value