Add String16#contains and strstr16 methods.

These are needed for aapt to find javadoc comments that contain
"@removed" in order to skip them when printing styleable docs.

Bug: 28663748
Change-Id: I8866d2167c41e11d6c2586da369560d5815fd13e
diff --git a/include/utils/String16.h b/include/utils/String16.h
index 9a67c7a..9bb6f0d 100644
--- a/include/utils/String16.h
+++ b/include/utils/String16.h
@@ -90,7 +90,9 @@
 
             bool                startsWith(const String16& prefix) const;
             bool                startsWith(const char16_t* prefix) const;
-            
+
+            bool                contains(const char16_t* chrs) const;
+
             status_t            makeLower();
 
             status_t            replaceAll(char16_t replaceThis,