Support dpi specific aapt flags.

With this support, you can set dpi-specific aapt flags like:
$(LOCAL_PACKAGE_NAME)_aapt_flags_hdpi := --version-code 100 \
                                         --version-name "100
which will override the --version-code and --version-name set in the
base apk's LOCAL_AAPT_FLAGS.

Bug := 18388705

Change-Id: Ie79d7b1b6bbf7463bce51ddae04ba81384ec58dc
diff --git a/core/dpi_specific_apk.mk b/core/dpi_specific_apk.mk
index aad4713..0e8cbdf 100644
--- a/core/dpi_specific_apk.mk
+++ b/core/dpi_specific_apk.mk
@@ -8,7 +8,7 @@
 
 # Set up all the target-specific variables.
 $(built_dpi_apk): PRIVATE_MODULE := $(dpi_apk_name)
-$(built_dpi_apk): PRIVATE_AAPT_FLAGS := $(LOCAL_AAPT_FLAGS) $(PRODUCT_AAPT_FLAGS)
+$(built_dpi_apk): PRIVATE_AAPT_FLAGS := $(LOCAL_AAPT_FLAGS) $(PRODUCT_AAPT_FLAGS) $($(LOCAL_PACKAGE_NAME)_aapt_flags_$(my_dpi))
 # Clear PRIVATE_PRODUCT_AAPT_CONFIG to include everything by default.
 $(built_dpi_apk): PRIVATE_PRODUCT_AAPT_CONFIG :=
 $(built_dpi_apk): PRIVATE_PRODUCT_AAPT_PREF_CONFIG := $(my_dpi)