open camera with O_RDWR.

This is somehow needed for Linux kernel 3.3 and above. If camera is opened with O_RDONLY, mmap will fail.
However, since we are not going to modify device memory, it should be allowed to open camera with O_RDONLY.

BUG=http://code.google.com/p/webrtc/issues/detail?id=512
Review URL: https://chromiumcodereview.appspot.com/10542080

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141308 0039d316-1c4b-4281-b951-d872f2087c98

media/video/capture/linux/video_capture_device_linux.cc

@@ -197,7 +197,8 @@ void VideoCaptureDeviceLinux::OnAllocate(int width,
 
   observer_ = observer;
 
-  if ((device_fd_ = open(device_name_.unique_id.c_str(), O_RDONLY)) < 0) {
+  // Need to open camera with O_RDWR after Linux kernel 3.3.
+  if ((device_fd_ = open(device_name_.unique_id.c_str(), O_RDWR)) < 0) {
     SetErrorState("Failed to open V4L2 device driver.");
     return;
   }