Make the Error class constructor protected

This is forcing to use Error::success(), which is in a wide majority
of cases a lot more readable.

Differential Revision: https://reviews.llvm.org/D26481

llvm-svn: 286561
diff --git a/lldb/source/Commands/CommandObjectDisassemble.cpp b/lldb/source/Commands/CommandObjectDisassemble.cpp
index 0795033..6273744 100644
--- a/lldb/source/Commands/CommandObjectDisassemble.cpp
+++ b/lldb/source/Commands/CommandObjectDisassemble.cpp
@@ -231,7 +231,7 @@
     ExecutionContext *execution_context) {
   if (!some_location_specified)
     current_function = true;
-  return Error();
+  return Error::success();
 }
 
 llvm::ArrayRef<OptionDefinition>
diff --git a/lldb/source/Commands/CommandObjectExpression.cpp b/lldb/source/Commands/CommandObjectExpression.cpp
index ba477cd..d98a3ee 100644
--- a/lldb/source/Commands/CommandObjectExpression.cpp
+++ b/lldb/source/Commands/CommandObjectExpression.cpp
@@ -303,7 +303,7 @@
     return Error("as it does not refer to a pointer");
   if (pointee.IsVoidType())
     return Error("as it refers to a pointer to void");
-  return Error();
+  return Error::success();
 }
 
 bool CommandObjectExpression::EvaluateExpression(const char *expr,