clang-format: Improve formatting of operators forced to new lines.

Before:
  unsigned ContentSize =
      sizeof(int16_t) // DWARF ARange version number
      +
      sizeof(int32_t) // Offset of CU in the .debug_info section
      +
      sizeof(int8_t) // Pointer Size (in bytes)
      +
      sizeof(int8_t); // Segment Size (in bytes)

After:
  unsigned ContentSize =
      sizeof(int16_t)   // DWARF ARange version number
      + sizeof(int32_t) // Offset of CU in the .debug_info section
      + sizeof(int8_t)  // Pointer Size (in bytes)
      + sizeof(int8_t); // Segment Size (in bytes)

This fixes llvm.org/PR17687.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194276 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/Format/FormatTest.cpp b/unittests/Format/FormatTest.cpp
index c0c7871..794fb1a 100644
--- a/unittests/Format/FormatTest.cpp
+++ b/unittests/Format/FormatTest.cpp
@@ -2668,6 +2668,14 @@
                "                    > ccccc) {\n"
                "}",
                Style);
+
+  // Forced by comments.
+  verifyFormat(
+      "unsigned ContentSize =\n"
+      "    sizeof(int16_t)   // DWARF ARange version number\n"
+      "    + sizeof(int32_t) // Offset of CU in the .debug_info section\n"
+      "    + sizeof(int8_t)  // Pointer Size (in bytes)\n"
+      "    + sizeof(int8_t); // Segment Size (in bytes)");
 }
 
 TEST_F(FormatTest, ConstructorInitializers) {