ART: Implement next-line assertions in Checker

Some tests require verifying an exact sequence of lines in the graph
dump. This was already possible by inserting 'CHECK-NOT: {{.*}}'
between the individual lines, but hardly a convenient way of doing so.
This patch introduces a new 'CHECK-NEXT' kind of assertions that
replaces the old method and will become useful for testing assembly.

Change-Id: I1bb951707bda44320166dc7ef828866a6957a113
diff --git a/tools/checker/match/test.py b/tools/checker/match/test.py
index e4dd784..348c1d2 100644
--- a/tools/checker/match/test.py
+++ b/tools/checker/match/test.py
@@ -195,6 +195,54 @@
       foo
     """)
 
+  def test_NextLineAssertions(self):
+    self.assertMatches(
+    """
+      // CHECK:      foo
+      // CHECK-NEXT: bar
+      // CHECK-NEXT: abc
+      // CHECK:      def
+    """,
+    """
+      foo
+      bar
+      abc
+      def
+    """)
+    self.assertMatches(
+    """
+      // CHECK:      foo
+      // CHECK-NEXT: bar
+      // CHECK:      def
+    """,
+    """
+      foo
+      bar
+      abc
+      def
+    """)
+    self.assertDoesNotMatch(
+    """
+      // CHECK:      foo
+      // CHECK-NEXT: bar
+    """,
+    """
+      foo
+      abc
+      bar
+    """)
+
+    self.assertDoesNotMatch(
+    """
+      // CHECK:      foo
+      // CHECK-NEXT: bar
+    """,
+    """
+      bar
+      foo
+      abc
+    """)
+
   def test_DagAssertions(self):
     self.assertMatches(
     """