Fix a DCHECK fired when switching between screen capturing and windown capturing.

content/browser/media/capture/desktop_capture_device.cc

Index: content/browser/media/capture/desktop_capture_device.cc
diff --git a/content/browser/media/capture/desktop_capture_device.cc b/content/browser/media/capture/desktop_capture_device.cc
index 246ab1b5d396557259a98af9fa6c012ae9205419..94e5084ddd42ca9e7b4b0ac2d4155d3bd528ee84 100644
--- a/content/browser/media/capture/desktop_capture_device.cc
+++ b/content/browser/media/capture/desktop_capture_device.cc
@@ -220,10 +220,14 @@ void DesktopCaptureDevice::Core::OnCaptureCompleted(
 
   base::TimeDelta capture_time(
       base::TimeDelta::FromMilliseconds(frame->capture_time_ms()));
-  UMA_HISTOGRAM_TIMES(
-      capturer_type_ == DesktopMediaID::TYPE_SCREEN ? kUmaScreenCaptureTime
-                                                    : kUmaWindowCaptureTime,
-      capture_time);
+
+  // The two UMA_ blocks must be put in its own scope since it creates a static
+  // variable which expected constant histogram name.
+  if (capturer_type_ == DesktopMediaID::TYPE_SCREEN) {
+    UMA_HISTOGRAM_TIMES(kUmaScreenCaptureTime, capture_time);
+  } else {
+    UMA_HISTOGRAM_TIMES(kUmaWindowCaptureTime, capture_time);
+  }
 
   scoped_ptr<webrtc::DesktopFrame> owned_frame(frame);