Enable cropping window capturing for Win7 when Aero is disabled.

webrtc/modules/desktop_capture/win/window_capture_utils.cc

Index: webrtc/modules/desktop_capture/win/window_capture_utils.cc
diff --git a/webrtc/modules/desktop_capture/win/window_capture_utils.cc b/webrtc/modules/desktop_capture/win/window_capture_utils.cc
index bfe7363f32d8c69b64a59e2388b47cb1a6c08ef5..bfa064d4d69ebca720ef589ba02277438b3ccf25 100644
--- a/webrtc/modules/desktop_capture/win/window_capture_utils.cc
+++ b/webrtc/modules/desktop_capture/win/window_capture_utils.cc
@@ -10,6 +10,8 @@
 
 #include "webrtc/modules/desktop_capture/win/window_capture_utils.h"
 
+#include "webrtc/base/criticalsection.h"
+
 namespace webrtc {
 
 bool
@@ -43,4 +45,29 @@ GetCroppedWindowRect(HWND window,
   return true;
 }
 
+bool IsAeroEnabled() {
+  typedef HRESULT (WINAPI *DwmIsCompositionEnabledFunc)(BOOL* enabled);
+
+  static rtc::GlobalLockPod lock;

[Sergey Ulanov, 2015/07/14 20:15:50]

I'm not sure it's safe to have this static inside the function. Make it global?

[jiayl2, 2015/07/14 22:25:32]

Removed

+  rtc::GlobalLockScope lock_scope(&lock);
+
+  static bool initialized = false;
+  static BOOL aero_enabled = FALSE;
+
+  if (!initialized) {
+    // Try to load dwmapi.dll dynamically since it is not available on XP.
+    HMODULE dwmapi_library = LoadLibrary(L"dwmapi.dll");
+    if (dwmapi_library) {
+      DwmIsCompositionEnabledFunc is_composition_enabled_func =
+          reinterpret_cast<DwmIsCompositionEnabledFunc>(
+              GetProcAddress(dwmapi_library, "DwmIsCompositionEnabled"));
+      is_composition_enabled_func(&aero_enabled);

[Sergey Ulanov, 2015/07/14 20:15:50]

You can store is_composition_enabled_func between IsAeroEnabled() calls, but you
should call it every time instead of remembering the result. Aero can be
enabled/disabled dynamically without restarting any applications.

[jiayl2, 2015/07/14 22:25:32]

The static method way doesn't work since it doesn't know when to free the
library.
Changed to use a object to hold the library/function.

+      FreeLibrary(dwmapi_library);
+    }
+    initialized = true;
+  }
+
+  return aero_enabled != FALSE;
+}
+
 }  // namespace webrtc