Fix gn suggest adding self-dependency loops.

Change-Id: I9663c1fd8533418f9d3a91d3baab01816a6a6964
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/25580
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: Matt Stark <msta@google.com>

src/gn/command_suggest.cc

diff --git a/src/gn/command_suggest.cc b/src/gn/command_suggest.cc
index 1f9a1e0..e88dffa 100644
--- a/src/gn/command_suggest.cc
+++ b/src/gn/command_suggest.cc
@@ -677,6 +677,14 @@
     OutputEditCommand(edit, included);
   }
 
+  // If a public header attempts to include a private header, we output "suggest
+  // making private header public". We also suggest depending on the target that
+  // declares the private header. If it's all within the same target though, we
+  // should stop here and not suggest adding the dependency.
+  if (includer == included) {
+    return result;
+  }
+
   // TODO: There are a bunch of optimizations we can perform here to make better
   // suggestions. They may be considered in the future. Some initial thoughts
   // include: