Refactor the Way Clients Obtain Interfaces from the Debug Client

The Windbg Extensions API is spread across multiple interfaces, making
a template based getter more convenient than statically defined
interface getters.

BUG=1168231

Change-Id: Id9789641074b842ebcb086d386c58fffabdf104a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637270Reviewed-by: Wei Li <weili@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Auto-Submit: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845207}

tools/win/chromeexts/chrome_exts_command.cc

@@ -20,9 +20,9 @@ HRESULT ChromeExtsCommand::Initialize(IDebugClient* debug_client,
   DCHECK(args);
   args_ = args;
   debug_client_ = debug_client;
-  HRESULT hr = debug_client_->QueryInterface(IID_PPV_ARGS(&debug_control_));
-  if (FAILED(hr)) {
-    return hr;
+  debug_control_ = GetDebugClientAs<IDebugControl>();
+  if (!debug_control_) {
+    return E_FAIL;
   }
   return S_OK;
 }

tools/win/chromeexts/chrome_exts_command.h

@@ -58,8 +58,14 @@ class ChromeExtsCommand {
   HRESULT PrintErrorV(const char* format, va_list ap);
 
   const std::string& args() const { return args_; }
-  IDebugClient* debug_client() { return debug_client_.Get(); }
-  IDebugControl* debug_control() { return debug_control_.Get(); }
+
+  // Returns the Debug Client as T, null ComPtr<T> otherwise.
+  template <typename T>
+  ComPtr<T> GetDebugClientAs() {
+    ComPtr<T> target_interface;
+    debug_client_.As(&target_interface);
+    return target_interface;
+  }
 
  private:
   std::string args_;

tools/win/chromeexts/commands/hwnd_command.cc

@@ -25,8 +25,8 @@ HRESULT HwndCommand::Execute() {
   // and truncate the displayed hwnds to 32-bit below.
   // See https://msdn.microsoft.com/en-us/library/aa384203.aspx
   DEBUG_VALUE value;
-  HRESULT hr = debug_control()->Evaluate(args().c_str(), DEBUG_VALUE_INT64,
-                                         &value, nullptr);
+  HRESULT hr = GetDebugClientAs<IDebugControl>()->Evaluate(
+      args().c_str(), DEBUG_VALUE_INT64, &value, nullptr);
   if (FAILED(hr)) {
     PrintErrorf("Unable to evaluate %s\n", args().c_str());
     return hr;