Selective build clobbering feature (landmines.py and android build scripts).

build/gyp_helper.py

Index: build/gyp_helper.py
diff --git a/build/gyp_helper.py b/build/gyp_helper.py
new file mode 100644
index 0000000000000000000000000000000000000000..69a341de4f61b852e193427410907579e90248d1
--- /dev/null
+++ b/build/gyp_helper.py
@@ -0,0 +1,50 @@
+# Copyright (c) 2012 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.
+
+# This file helps gyp_chromium and landmines correctly set up the gyp
+# environment from chromium.gyp_env on disk
+
+import os
+
+SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
+CHROME_SRC = os.path.dirname(SCRIPT_DIR)
+
+
+def apply_gyp_environment_from_file(file_path):
+  """Reads in a *.gyp_env file and applies the valid keys to os.environ."""
+  if not os.path.exists(file_path):
+    return
+  with open(file_path) as f:
+    file_contents = f.read()
+  try:
+    file_data = eval(file_contents, {'__builtins__': None}, None)
+  except SyntaxError, e:
+    e.filename = os.path.abspath(file_path)
+    raise
+  supported_vars = (
+      'CC',
+      'CHROMIUM_GYP_FILE',
+      'CHROMIUM_GYP_SYNTAX_CHECK',
+      'CXX',
+      'GYP_DEFINES',
+      'GYP_GENERATOR_FLAGS',
+      'GYP_GENERATOR_OUTPUT',
+      'GYP_GENERATORS',
+  )
+  for var in supported_vars:
+    file_val = file_data.get(var)
+    if file_val:
+      if var in os.environ:
+        print 'INFO: Environment value for "%s" overrides value in %s.' % (
+            var, os.path.abspath(file_path)
+        )
+      else:
+        os.environ[var] = file_val
+
+
+def apply_chromium_gyp_env():
+  if 'SKIP_CHROMIUM_GYP_ENV' not in os.environ:
+    # Update the environment based on chromium.gyp_env
+    path = os.path.join(os.path.dirname(CHROME_SRC), 'chromium.gyp_env')
+    apply_gyp_environment_from_file(path)