Simplify ClassLinker::LoadClass

Starting out by removing the ClassLinker::LoadClass to not take a
DexFile. Then started pulling threads so that ClassLinker::LoadClass
could take a StringPiece instead of const char*. Finally went through
and removed all uses of StringPiece::data() to make sure things are
clean.

Change-Id: I47cfa0e8e0e35a31e0ebbd0f7d6a105be83ebe88
diff --git a/src/object.h b/src/object.h
index cd57460..aec8c34 100644
--- a/src/object.h
+++ b/src/object.h
@@ -507,7 +507,7 @@
   // Returns true if this class is in the same packages as that class.
   bool IsInSamePackage(const Class* that) const;
 
-  static bool IsInSamePackage(const char* descriptor1, const char* descriptor2);
+  static bool IsInSamePackage(const StringPiece& descriptor1, const StringPiece& descriptor2);
 
   // Returns true if this class represents an array class.
   bool IsArray() const {