Enable IntLongMath checker of error prone

- This checker avoid that an expression of type int may
overflow before being assigned to a long.
- Do not longer use long where it is not needed since an
integer can be used from a dex specification point of view.

Bug:
Change-Id: I392a1f79f0c89659bcb02063be4233ea1b104eb3
diff --git a/build.gradle b/build.gradle
index 6dadb5c..35da63e 100644
--- a/build.gradle
+++ b/build.gradle
@@ -19,7 +19,8 @@
     '-Xep:OperatorPrecedence:WARN',
     '-Xep:RemoveUnusedImports:WARN',
     '-Xep:MissingOverride:WARN',
-    '-Xep:OvershadowingSubclassFields:WARN']
+    '-Xep:OvershadowingSubclassFields:WARN',
+    '-Xep:IntLongMath:WARN']
 
 apply from: 'copyAdditionalJctfCommonFiles.gradle'