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/stringpiece.h b/src/stringpiece.h
index 6a5c60b..249b041 100644
--- a/src/stringpiece.h
+++ b/src/stringpiece.h
@@ -143,10 +143,10 @@
 
   int copy(char* buf, size_type n, size_type pos = 0) const;
 
-  int find(const StringPiece& s, size_type pos = 0) const;
-  int find(char c, size_type pos = 0) const;
-  int rfind(const StringPiece& s, size_type pos = npos) const;
-  int rfind(char c, size_type pos = npos) const;
+  size_type find(const StringPiece& s, size_type pos = 0) const;
+  size_type find(char c, size_type pos = 0) const;
+  size_type rfind(const StringPiece& s, size_type pos = npos) const;
+  size_type rfind(char c, size_type pos = npos) const;
 
   StringPiece substr(size_type pos, size_type n = npos) const;
 };