[Android] Only set recommended flags if they are unset

build/android/developer_recommended_flags.gypi

 # Copyright 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.
 
 # This is the set of recommended gyp variable settings for Chrome for Android development.
 #
-# These can be used by copying them into ~/.gyp/include.gypi or $CHROME_SRC/chrome/supplement.gypi
-# Even better, use the below in chrome/supplement.gypi:
+# These can be used by copying this file to $CHROME_SRC/chrome/supplement.gypi.

[Yaron, 2013/04/19 22:44:27]

Why encourage people to use chrome/supplement.gypi when it'll cause a dirty tree
and may accidentally get included in the commit? ISTM that the home-dir approach
is safer.

[cjhopman, 2013/04/19 22:51:19]

chrome/supplement.gypi is ignored in .gitignore specifically so that it can be
used for user-specified, per-repo settings. Also using chrome/supplement.gypi
allows including this file directly.

+#
+# Even better, create chrome/supplement.gypi containing the following:
 #   {
 #     'includes': [ '../build/android/developer_recommended_flags.gypi' ]
 #   }
 # and you'll get new settings automatically.
+# When using this method, you can override individual settings by setting them unconditionally (with
+# no %) in chrome/supplement.gypi.
+# I.e. to disable optimize_jni_generation but use everything else:
+#   {
+#     'variables': {
+#       'optimize_jni_generation': 0,
+#     },
+#     'includes': [ '../build/android/developer_recommended_flags.gypi' ]
+#   }
 
 {
   'variables': {
     # When set to 1, only write jni generated files if they've changed. This can prevent unnecessary
     # compiling/linking of native libraries when editing java files.
-    'optimize_jni_generation': 1,
+    'optimize_jni_generation%': 1,
 
     # Set component to 'shared_library' to enable the component build. This builds native code as
     # many small shared libraries instead of one monolithic library. This slightly reduces the time
     # required for incremental builds.
-    'component': 'shared_library',
+    'component%': 'shared_library',
 
     # When gyp_managed_install is set to 1, building an APK will install that APK on the connected
     # device(/emulator). To install on multiple devices (or onto a new device), build the APK once
     # with each device attached. This greatly reduces the time required for incremental builds.
     #
     # This comes with some caveats:
     #   Only works with a single device connected.
     #   Some actions are always run (i.e. ninja will never say "no work to do").
     #   Native libraries are not packaged in the APK (you can not manually install the APK)
-    'gyp_managed_install': 1,
+    'gyp_managed_install%': 1,
 
     # Set clang to 1 to use the clang compiler. Clang has much (much, much) better warning/error
     # messages than gcc.
     # TODO(cjhopman): Enable this when http://crbug.com/156420 is addressed. Until then, users can
     # set clang to 1, but Android stack traces will sometimes be incomplete.
-    #'clang': 1,
+    #'clang%': 1,
+
+    # Set fastbuild to 1 to build with less debugging information. This can greatly decrease linking
+    # time. The downside is that stack traces will be missing useful information (like line
+    # numbers).
+    #'fastbuild%': 1,
   },
 }