Fix clang-tidy warnings in aapt and aapt2.

* Add explicit keyword to conversion constructors.
* Add NOLINT(implicit) comments for implicit conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
* Use const reference type to avoid unnecessary copy.
Bug: 30413862
Test: build with WITH_TIDY=1

Change-Id: Id6d21961f313a1ad92b15a37fdaa5be9e8ab48e1
diff --git a/tools/aapt/XMLNode.cpp b/tools/aapt/XMLNode.cpp
index 5b215da..15ec4af 100644
--- a/tools/aapt/XMLNode.cpp
+++ b/tools/aapt/XMLNode.cpp
@@ -67,7 +67,7 @@
 static const String16 RESOURCES_PRV_PREFIX(RESOURCES_ROOT_PRV_NAMESPACE);
 static const String16 RESOURCES_TOOLS_NAMESPACE("http://schemas.android.com/tools");
 
-String16 getNamespaceResourcePackage(String16 appPackage, String16 namespaceUri, bool* outIsPublic)
+String16 getNamespaceResourcePackage(const String16& appPackage, const String16& namespaceUri, bool* outIsPublic)
 {
     //printf("%s starts with %s?\n", String8(namespaceUri).string(),
     //       String8(RESOURCES_PREFIX).string());
@@ -98,7 +98,7 @@
 
 status_t hasSubstitutionErrors(const char* fileName,
                                ResXMLTree* inXml,
-                               String16 str16)
+                               const String16& str16)
 {
     const char16_t* str = str16.string();
     const char16_t* p = str;