Make the gn copy() tool honor dependencies.

tools/gn/ninja_copy_target_writer.cc

Index: tools/gn/ninja_copy_target_writer.cc
diff --git a/tools/gn/ninja_copy_target_writer.cc b/tools/gn/ninja_copy_target_writer.cc
index ca3485240854cd8147600fb838e36c19918df64a..57dc8778f40fda1ff3ab4c48f306160836440853 100644
--- a/tools/gn/ninja_copy_target_writer.cc
+++ b/tools/gn/ninja_copy_target_writer.cc
@@ -71,6 +71,9 @@ void NinjaCopyTargetWriter::WriteCopyRules(
       GetNinjaRulePrefixForToolchain(settings_) +
       Toolchain::ToolTypeToName(Toolchain::TYPE_COPY);
 
+  OutputFile input_dep =
+      WriteInputDepsStampAndGetDep(std::vector<const Target*>());

[Dirk Pranke, 2014/10/30 02:22:19]

I just stole this from ninja_binary_target_writer; it's not clear to me if using
a stamp file for this is the right thing to do, though (vs. just writing out the
dependencies directly).

Also, it's not clear to me if this'll cause other dependencies to get written?
(I didn't write any tests for this yet or look at any existing tests).

+
   // Note that we don't write implicit deps for copy steps. "copy" only
   // depends on the output files themselves, rather than having includes
   // (the possibility of generated #includes is the main reason for implicit
@@ -104,6 +107,10 @@ void NinjaCopyTargetWriter::WriteCopyRules(
     path_output_.WriteFile(out_, output_file);
     out_ << ": " << tool_name << " ";
     path_output_.WriteFile(out_, input_file);
+    if (!input_dep.value().empty()) {
+      out_ << " || ";
+      path_output_.WriteFile(out_, input_dep);
+    }
     out_ << std::endl;
   }
 }