[CrOS Cellular] Update FakeNetworkActivationHandler.

This CL adds some clarifying comments and makes some functions const.
These ideas were suggested as part of a similar CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1602072

Bug: 961084
Change-Id: Id34b3b960d8f1a86eaa930df2836e0f836ea9d5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1603489
Auto-Submit: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658289}

chromeos/network/fake_network_activation_handler.cc

@@ -32,13 +32,14 @@ FakeNetworkActivationHandler::ActivationParams::ActivationParams(
 
 FakeNetworkActivationHandler::ActivationParams::~ActivationParams() = default;
 
-void FakeNetworkActivationHandler::ActivationParams::InvokeSuccessCallback() {
+void FakeNetworkActivationHandler::ActivationParams::InvokeSuccessCallback()
+    const {
   success_callback_.Run();
 }
 
 void FakeNetworkActivationHandler::ActivationParams::InvokeErrorCallback(
     const std::string& error_name,
-    std::unique_ptr<base::DictionaryValue> error_data) {
+    std::unique_ptr<base::DictionaryValue> error_data) const {
   error_callback_.Run(error_name, std::move(error_data));
 }
 

chromeos/network/fake_network_activation_handler.h

@@ -21,6 +21,8 @@ class COMPONENT_EXPORT(CHROMEOS_NETWORK) FakeNetworkActivationHandler
   FakeNetworkActivationHandler();
   ~FakeNetworkActivationHandler() override;
 
+  // Parameters captured by calls to Activate() and CompleteActivation().
+  // Accessible to clients via activate_calls() and complete_activation_calls().
   class ActivationParams {
    public:
     // For Activate() calls.
@@ -38,11 +40,15 @@ class COMPONENT_EXPORT(CHROMEOS_NETWORK) FakeNetworkActivationHandler
     ~ActivationParams();
 
     const std::string& service_path() const { return service_path_; }
+
+    // Should only be called on ActivationParams objects corresponding to
+    // Activate() calls.
     const std::string& carrier() const { return *carrier_; }
 
-    void InvokeSuccessCallback();
-    void InvokeErrorCallback(const std::string& error_name,
-                             std::unique_ptr<base::DictionaryValue> error_data);
+    void InvokeSuccessCallback() const;
+    void InvokeErrorCallback(
+        const std::string& error_name,
+        std::unique_ptr<base::DictionaryValue> error_data) const;
 
    private:
     std::string service_path_;
@@ -51,8 +57,10 @@ class COMPONENT_EXPORT(CHROMEOS_NETWORK) FakeNetworkActivationHandler
     network_handler::ErrorCallback error_callback_;
   };
 
-  std::vector<ActivationParams>& activate_calls() { return activate_calls_; }
-  std::vector<ActivationParams>& complete_activation_calls() {
+  const std::vector<ActivationParams>& activate_calls() const {
+    return activate_calls_;
+  }
+  const std::vector<ActivationParams>& complete_activation_calls() const {
     return complete_activation_calls_;
   }