[clang-format] Use number of unwrapped lines for short namespace

Summary:
This patch makes the namespace comment fixer use the number of unwrapped lines
that a namespace spans to detect it that namespace is short, thus not needing
end comments to be added.
This is needed to ensure clang-format is idempotent. Previously, a short namespace
was detected by the original source code lines. This has the effect of requiring two
runs for this example:
```
namespace { class A; }
```
after first run:
```
namespace {
class A;
}
```
after second run:
```
namespace {
class A;
} // namespace
```

Reviewers: djasper

Reviewed By: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D30528

llvm-svn: 296736
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 30cc749..7ab0c75 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -185,7 +185,7 @@
   EXPECT_EQ("namespace N {\n"
             "\n"
             "int i;\n"
-            "}  // namespace N",
+            "}",
             format("namespace N {\n"
                    "\n"
                    "int    i;\n"
@@ -281,8 +281,7 @@
                    "}", LLVMWithNoNamespaceFix));
   EXPECT_EQ("namespace {\n"
             "int i;\n"
-            "\n"
-            "} // namespace",
+            "}",
             format("namespace {\n"
                    "int i;\n"
                    "\n"
@@ -5460,7 +5459,7 @@
   EXPECT_EQ("namespace N {\n"
             "void f() {}\n"
             "void g()\n"
-            "}",
+            "} // namespace N",
             format("namespace N  { void f( ) { } void g( ) }"));
 }
 
@@ -6140,8 +6139,8 @@
                "  void f() {}\n"
                "  int *a;\n"
                "};\n"
-               "}\n"
-               "}");
+               "} // namespace b\n"
+               "} // namespace a");
 }
 
 TEST_F(FormatTest, SpecialTokensAtEndOfLine) {
@@ -7934,7 +7933,7 @@
                "struct B {\n"
                "  int x;\n"
                "};\n"
-               "}\n",
+               "} // namespace a\n",
                StroustrupBraceStyle);
 
   verifyFormat("void foo()\n"