Fix build break from generating robo test code coverage

Use absolute path for LOCAL_INSTRUMENT_SOURCE_DIRS, because Jacoco fail
to get the source code path to parse the code coverage.

Test step:
1. tapas RunLauncherRoboTests
2. make -j30 dist (Make sure RunLauncherRoboTests does not break)
3. make -j30 RunLauncherRoboTests-jacoco dist
4. See the coverage report

Bug: 149001617
Change-Id: If82a839ae52c20c7eb269090976de05fa5d462c4
diff --git a/robolectric_tests/Android.mk b/robolectric_tests/Android.mk
index 6059981..7c7e73c 100644
--- a/robolectric_tests/Android.mk
+++ b/robolectric_tests/Android.mk
@@ -52,7 +52,7 @@
 
 LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res
 LOCAL_TEST_PACKAGE := Launcher3
-LOCAL_INSTRUMENT_SOURCE_DIRS := $(dir $(LOCAL_PATH))../src
+LOCAL_INSTRUMENT_SOURCE_DIRS := packages/apps/Launcher3/src
 
 LOCAL_ROBOTEST_TIMEOUT := 36000