aidl-cpp: Add support for hex values in const int

Add support for hex values in 'const int' definitions in aidl.

BUG: 26936964
TEST: Added/Ran unit tests & integration tests.
Change-Id: I2e94a4f9a03b46eb02aae29120afc9e8f15e71c8
diff --git a/aidl.cpp b/aidl.cpp
index dea559a..513aaee 100644
--- a/aidl.cpp
+++ b/aidl.cpp
@@ -422,6 +422,8 @@
       success = false;
     }
     names.insert(int_constant->GetName());
+    // We've logged an error message for this on object construction.
+    success = success && int_constant->IsValid();
   }
   for (const std::unique_ptr<AidlStringConstant>& string_constant :
        interface.GetStringConstants()) {