[gcc] Fix build failure caused by error: multi-line comment [-Werror=comment]...

[gcc] Fix build failure caused by error: multi-line comment [-Werror=comment] in focus_traversal_unittest.cc

gcc toolchain throws a warning for using a trailing '\' in a comment which begins with '//'.

clang toolchain doesn't throw any warning for this hence its not captured by our bots.

Compiler option -Wno-comment appended after -Wall fixes the above issue but results in having inconsistent
comments.

The code snippet at [1] cleverly avoids these warnings as shown.

[1] https://code.google.com/p/chromium/codesearch#chromium/src/extensions/browser/content_hash_tree.h&l=23

R=mgiuca@chromium.org
TBR=sky@chromium.org

Review URL: https://codereview.chromium.org/874663003

Cr-Commit-Position: refs/heads/master@{#314745}

ui/views/focus/focus_traversal_unittest.cc

@@ -795,19 +795,19 @@ void FocusTraversalNonFocusableTest::InitContentView() {
   // the x1-x3-x2 triangles, it will traverse the left sibling of x1, (x+1)0,
   // twice, which means it will visit O(2^n) nodes.)
   //
-  //              0
-  //            /   \
-  //          /       \
-  //         10        1
-  //        /  \      / \
-  //      /      \   /   \
-  //     20      11  2   3
-  //    / \      / \
-  //   /   \    /   \
-  //  ...  21  12   13
-  //       / \
-  //      /   \
-  //     22   23
+  // |              0         |
+  // |            /   \       |
+  // |          /       \     |
+  // |         10        1    |
+  // |        /  \      / \   |
+  // |      /      \   /   \  |
+  // |     20      11  2   3  |
+  // |    / \      / \        |
+  // |   /   \    /   \       |
+  // |  ...  21  12   13      |
+  // |       / \              |
+  // |      /   \             |
+  // |     22   23            |
 
   View* v = GetContentsView();
   // Create 30 groups of 4 nodes. |v| is the top of each group.