android: Add a way to override build system variables.

pylib/gyp/generator/android.py

Index: pylib/gyp/generator/android.py
diff --git a/pylib/gyp/generator/android.py b/pylib/gyp/generator/android.py
index d7aa9029deae81f1db4002ab1e3f689cccb1bcbe..a2a3af4b5f6abf7c885195c65e1d775803d8e532 100644
--- a/pylib/gyp/generator/android.py
+++ b/pylib/gyp/generator/android.py
@@ -50,6 +50,8 @@ generator_supports_multiple_toolsets = True
 generator_additional_non_configuration_keys = [
     # Boolean to declare that this target does not want its name mangled.
     'android_unmangled_name',
+    # Map of android build system variables to set.
+    'android_build_settings',
 ]
 generator_additional_path_sections = []
 generator_extra_sources_for_rules = []
@@ -849,6 +851,16 @@ class AndroidMkWriter(object):
     if self.type != 'none':
       self.WriteTargetFlags(spec, configs, link_deps)
 
+    settings = spec.get('android_build_settings', {})

[Primiano Tucci (use gerrit), 2014/09/12 12:22:52]

Are you deliberately emitting this before all the LOCAL_ ... makefile stuff? I
thought you planned to emit the overrides after.

[Torne, 2014/09/12 13:13:04]

This is at the end; this is the function that emits the final "include
$(BUILD_STATIC_LIBRARY)" or whichever.

+    if settings:
+      self.WriteLn('### Manually overridden build settings')

[Primiano Tucci (use gerrit), 2014/09/12 12:22:52]

I'd mention android_build_settings here.
Reading that in a .mk would make me feel as if somebody manually hacked the
makefile.

[Torne, 2014/09/12 13:13:04]

Yeah, good point, I'll change it.

+      for k, v in settings.iteritems():
+        if isinstance(v, list):
+          self.WriteList(v, k)
+        else:
+          self.WriteLn('%s := %s' % (k, make.QuoteIfNecessary(v)))
+      self.WriteLn('')
+
     # Add to the set of targets which represent the gyp 'all' target. We use the
     # name 'gyp_all_modules' as the Android build system doesn't allow the use
     # of the Make target 'all' and because 'all_modules' is the equivalent of