Fix clang-tidy warnings in libs/hwui.

* Add explicit keyword to conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
Test: build with WITH_TIDY=1

Change-Id: Iab3e6636f60a70cb124f29dc19f20f842fa8dfda
diff --git a/tools/aapt/AaptAssets.h b/tools/aapt/AaptAssets.h
index 4fdc964..eadd48a 100644
--- a/tools/aapt/AaptAssets.h
+++ b/tools/aapt/AaptAssets.h
@@ -103,7 +103,7 @@
 {
 public:
     AaptGroupEntry() {}
-    AaptGroupEntry(const ConfigDescription& config) : mParams(config) {}
+    explicit AaptGroupEntry(const ConfigDescription& config) : mParams(config) {}
 
     bool initFromDirName(const char* dir, String8* resType);
 
@@ -312,7 +312,7 @@
         : isPublic(false), isJavaSymbol(false), typeCode(TYPE_UNKNOWN)
     {
     }
-    AaptSymbolEntry(const String8& _name)
+    explicit AaptSymbolEntry(const String8& _name)
         : name(_name), isPublic(false), isJavaSymbol(false), typeCode(TYPE_UNKNOWN)
     {
     }