Check for inputs not generated by deps

tools/gn/target.h

Index: tools/gn/target.h
diff --git a/tools/gn/target.h b/tools/gn/target.h
index 00500489923ddec832ede0ea067eb9f0183b5b83..58319f121e596209e3c9084aecfe029eb999f8fb 100644
--- a/tools/gn/target.h
+++ b/tools/gn/target.h
@@ -221,6 +221,16 @@ class Target : public Item {
   // frequently by unit tests which become needlessly verbose.
   bool SetToolchain(const Toolchain* toolchain, Err* err = nullptr);
 
+  // Once this target has been resolved, all outputs from the target will be
+  // listed here. This will include things listed in the "outputs" for an
+  // action or a copy step, and the output library or executable file(s) from
+  // binary targets.
+  //
+  // It will NOT include stamp files and object files.
+  const std::vector<OutputFile>& computed_outputs() const {
+    return computed_outputs_;
+  }
+
   // Returns outputs from this target. The link output file is the one that
   // other targets link to when they depend on this target. This will only be
   // valid for libraries and will be empty for all other target types.
@@ -260,6 +270,8 @@ class Target : public Item {
   bool CheckVisibility(Err* err) const;
   bool CheckTestonly(Err* err) const;
   bool CheckNoNestedStaticLibs(Err* err) const;
+  void CheckSourcesGenerated() const;
+  void CheckSourceGenerated(const SourceFile& source) const;
 
   OutputType output_type_;
   std::string output_name_;
@@ -304,7 +316,8 @@ class Target : public Item {
   // Toolchain used by this target. Null until target is resolved.
   const Toolchain* toolchain_;
 
-  // Output files. Null until the target is resolved.
+  // Output files. Empty until the target is resolved.
+  std::vector<OutputFile> computed_outputs_;
   OutputFile link_output_file_;
   OutputFile dependency_output_file_;