clang/win: Fix compile error.

Const member variables must be set in constructors.

BUG=82385
TBR=perkj

Review URL: https://codereview.chromium.org/917183003

Cr-Commit-Position: refs/heads/master@{#316281}

media/video/capture/win/capability_list_win.h

@@ -18,7 +18,7 @@ namespace media {
 
 struct CapabilityWin {
   CapabilityWin(int index, const VideoCaptureFormat& format)
-      : stream_index(index), supported_format(format) {}
+      : stream_index(index), supported_format(format), info_header() {}
 
   // Used by VideoCaptureDeviceWin.
   CapabilityWin(int index, const VideoCaptureFormat& format,