cmake: add command line options to output script profiling data

For users of CMake who want to optimize their scripts if they take a
while to run, this commit adds the ability to output profiling data.

To enable this output, it adds the two command line parameters
to select the output path and format.

This commit adds the first profiling format of type ``google-trace``,
which is the output is a JSON file containing Duration events as per the
Google Trace Format specification:

https://docs.google.com/document/d/1CvAClvFfyA5R-
PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview#

1 files changed, 29 insertions, 0 deletions

diff --git a/Source/cmMakefileProfilingData.h b/Source/cmMakefileProfilingData.h
new file mode 100644
index 0000000..1babd97
--- /dev/null
+++ b/Source/cmMakefileProfilingData.h
@@ -0,0 +1,29 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#ifndef cmMakefileProfilingData_h
+#define cmMakefileProfilingData_h
+#include <memory>
+#include <string>
+
+#include "cmsys/FStream.hxx"
+
+namespace Json {
+class StreamWriter;
+}
+
+class cmListFileContext;
+struct cmListFileFunction;
+
+class cmMakefileProfilingData
+{
+public:
+  cmMakefileProfilingData(const std::string&);
+  ~cmMakefileProfilingData() noexcept;
+  void StartEntry(const cmListFileFunction& lff, cmListFileContext const& lfc);
+  void StopEntry();
+
+private:
+  cmsys::ofstream ProfileStream;
+  std::unique_ptr<Json::StreamWriter> JsonWriter;
+};
+#endif