Add module level qpl logging. (pytorch#30906)

Summary:
Pull Request resolved: pytorch#30906

Add mobile module observer to measure performance of each method run.
ghstack-source-id: 95120194

Test Plan:
Run pytext model through BI cloaking flow on lite-interpreter and verify logs are sent:
1. buck install -r fb4a
2. Go to internal setting and find MobileConfig, search for android_bi_infra_cloaking_iab_models and set the following params:
a. sample_rate: 1.0
b. enabled: true
c. use_bytedoc_pytorch_model: true
d. use_bytedoc_caffe2_model: false
e. use_full_jit: false
3. Go back to new feed and scroll down until find an ads which will direct you to offsite webpage;
4. Click on the ads, wait for the offsite ads loads;
5. Click back to news feed;
6. Go to scuba table: https://fburl.com/scuba/4fghwp0b and see all the operator runs have been logged:

{F223456981}

Reviewed By: ljk53

Differential Revision: D18702116

fbshipit-source-id: a9f07eee684e3022cef5ba3c5934f30f20192a85

Author: xcheng16

torch/csrc/jit/mobile/module.cpp

@@ -28,12 +28,24 @@ c10::IValue Module::run_method(const std::string& method_name, Stack stack) {
   debug_info->setModelName(name());
   debug_info->setMethodName(method_name);
   at::setThreadLocalDebugInfo(debug_info);
+
+  auto observer = torch::observerConfig().getModuleObserver();
+  if (observer) {
+    observer->onEnter();
+  }
 #endif
 
   auto m = find_method(method_name);
   stack.insert(stack.begin(), object_);
   m->run(stack);
-  return stack.front();
+  c10::IValue result = stack.front();
+
+#if defined(PYTORCH_MOBILE_OBSERVER)
+  if (observer) {
+    observer->onExit();
+  }
+#endif
+  return result;
 }
 
 Function* Module::find_method(const std::string& basename) const {

torch/csrc/jit/mobile/observer.cpp

@@ -0,0 +1,10 @@
+#include <torch/csrc/jit/mobile/observer.h>
+
+namespace torch {
+
+MobileObserverConfig& observerConfig() {
+  static MobileObserverConfig instance;
+  return instance;
+}
+
+} // namespace torch

torch/csrc/jit/mobile/observer.h

@@ -2,6 +2,7 @@
 
 #include <string>
 #include <ATen/ThreadLocalDebugInfo.h>
+
 namespace torch {
 
 class MobileDebugInfo
@@ -39,4 +40,27 @@ class MobileDebugInfo
   size_t op_idx_ = 0;
 };
 
+class MobileModuleObserver {
+    public:
+    virtual ~MobileModuleObserver() = default;
+
+    virtual void onEnter() {}
+    virtual void onExit() {}
+};
+
+class MobileObserverConfig {
+  public:
+  void setModuleObserver(std::unique_ptr<MobileModuleObserver> reporter) {
+    module_observer_ = std::move(reporter);
+  }
+  MobileModuleObserver* getModuleObserver() {
+    return module_observer_.get();
+  }
+
+private:
+  std::unique_ptr<MobileModuleObserver> module_observer_;
+};
+
+MobileObserverConfig& observerConfig();
+
 } // namespace torch