[ASTMatcher] Add a node matcher for EnumType.

[aaron.ballman]

LGTM!

docs/LibASTMatchersReference.html

Given
   class C c;
   N::M::D d;
 
 elaboratedType() matches the type of the variable declarations of both
 c and d.
 </pre></td></tr>
 
 
+<tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1Type.html">Type</a>&gt;</td><td class="name" onclick="toggle('enumType0')"><a name="enumType0Anchor">enumType</a></td><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1EnumType.html">EnumType</a>&gt;...</td></tr>
+<tr><td colspan="4" class="doc" id="enumType0"><pre>Matches enum types.
+
+Given
+  enum C { Green };
+  enum S { Red };
+
+  C c;
+  S s;
+
+enumType() matches the type of the variable declarations of both c and
+s.
+</pre></td></tr>
+
+
 <tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1Type.html">Type</a>&gt;</td><td class="name" onclick="toggle('functionProtoType0')"><a name="functionProtoType0Anchor">functionProtoType</a></td><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1FunctionProtoType.html">FunctionProtoType</a>&gt;...</td></tr>
 <tr><td colspan="4" class="doc" id="functionProtoType0"><pre>Matches FunctionProtoType nodes.
 
 Given
   int (*f)(int);
   void g();
 functionProtoType()
   matches "int (*f)(int)" and the type of "g" in C++ mode.

include/clang/ASTMatchers/ASTMatchers.h

 /// Given
 /// \code
 ///   typedef int X;
 /// \endcode
 /// typedefType()
 ///   matches "typedef int X"
 AST_TYPE_MATCHER(TypedefType, typedefType);
 
+/// \brief Matches enum types.
+///
+/// Given
+/// \code
+///   enum C { Green };
+///   enum class S { Red };
+///
+///   C c;
+///   S s;
+/// \endcode
+//
+/// \c enumType() matches the type of the variable declarations of both \c c and
+/// \c s.
+AST_TYPE_MATCHER(EnumType, enumType);
+
 /// \brief Matches template specialization types.
 ///
 /// Given
 /// \code
 ///   template <typename T>
 ///   class C { };
 ///
 ///   template class C<int>;  // A

lib/ASTMatchers/Dynamic/Registry.cpp

RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(dependentSizedArrayType);
   REGISTER_MATCHER(designatedInitExpr);
   REGISTER_MATCHER(designatorCountIs);
   REGISTER_MATCHER(doStmt);
   REGISTER_MATCHER(eachOf);
   REGISTER_MATCHER(elaboratedType);
   REGISTER_MATCHER(enumConstantDecl);
   REGISTER_MATCHER(enumDecl);
+  REGISTER_MATCHER(enumType);
   REGISTER_MATCHER(equalsBoundNode);
   REGISTER_MATCHER(equalsIntegralValue);
   REGISTER_MATCHER(explicitCastExpr);
   REGISTER_MATCHER(expr);
   REGISTER_MATCHER(exprWithCleanups);
   REGISTER_MATCHER(fieldDecl);
   REGISTER_MATCHER(floatLiteral);
   REGISTER_MATCHER(forEach);

unittests/ASTMatchers/ASTMatchersNodeTest.cpp

TEST(TypeMatching, AutoRefTypes) {
   EXPECT_TRUE(matches(Fragment, varDecl(hasName("e"),
                                         hasType(referenceType()))));
   EXPECT_TRUE(notMatches(Fragment, varDecl(hasName("e"),
                                            hasType(lValueReferenceType()))));
   EXPECT_TRUE(matches(Fragment, varDecl(hasName("e"),
                                         hasType(rValueReferenceType()))));
 }
 
+TEST(TypeMatching, MatchesEnumTypes) {
+  EXPECT_TRUE(matches("enum Color { Green }; Color color;",
+                      loc(enumType())));
+  EXPECT_TRUE(matches("enum class Color { Green }; Color color;",
+                      loc(enumType())));
+}
+
 TEST(TypeMatching, MatchesPointersToConstTypes) {
   EXPECT_TRUE(matches("int b; int * const a = &b;",
                       loc(pointerType())));
   EXPECT_TRUE(matches("int b; int * const a = &b;",
                       loc(pointerType())));
   EXPECT_TRUE(matches(
     "int b; const int * a = &b;",
     loc(pointerType(pointee(builtinType())))));