SDK: source.properties templates.

This adds support for "templates" source.properties files that can
inherit the platform version/codename/api level from the build.

The purpose is for a given build to always generate SDK files that
match the platform generated in the same branch.

Change-Id: Id623bbef45a04d953da8eade7e8c34c77709f9c3
diff --git a/sdk/platform_source.prop_template b/sdk/platform_source.prop_template
new file mode 100644
index 0000000..17a5e4e
--- /dev/null
+++ b/sdk/platform_source.prop_template
@@ -0,0 +1,9 @@
+Pkg.Desc=Android SDK Platform ${PLATFORM_VERSION}
+Pkg.UserSrc=false
+Platform.Version=${PLATFORM_VERSION}
+Pkg.Revision=1
+AndroidVersion.ApiLevel=${PLATFORM_SDK_VERSION}
+AndroidVersion.CodeName=${PLATFORM_VERSION_CODENAME}
+Layoutlib.Api=7
+Layoutlib.Revision=1
+Platform.MinToolsRev=15