[ASTImporter] Implement some expression-related AST node import (part 2)

* Some code cleanup
* Add tests not present in http://reviews.llvm.org/D14286
* Integrate a test suite from Serge Pavlov (http://reviews.llvm.org/D14224)
* ArrayTypeTraitExpr: serialize sub-expression to avoid keeping it undefined
* Implement import of some nodes:
  - ArrayTypeTraitExpr
  - ExpressionTraitExpr
  - OpaqueValueExpr
  - ArraySubscriptExpr
  - ExplicitCastExpr
  - ImplicitValueInitExpr
  - OffsetOfExpr
  - CXXThisExpr
  - CXXThrowExpr
  - CXXNoexceptExpr
  - CXXDefaultArgExpr
  - CXXScalarValueInitExpr
  - CXXBindTemporaryExpr
  - CXXTemporaryObjectExpr
  - MaterializeTemporaryExpr
  - ExprWithCleanups

  - StaticAssertDecl
  - FriendDecl

  - DecayedType

Differential Revision: https://reviews.llvm.org/D14326

llvm-svn: 282572
diff --git a/clang/test/ASTMerge/class2.cpp b/clang/test/ASTMerge/class2.cpp
new file mode 100644
index 0000000..6021403
--- /dev/null
+++ b/clang/test/ASTMerge/class2.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++1z -emit-pch -o %t.1.ast %S/Inputs/class3.cpp
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++1z -ast-merge %t.1.ast -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+class C3 {
+  int method_1(C2 *x) {
+    return x->x;
+  }
+};