Pepper: Add IsAvailable() static methods to C++ wrappers to AudioInput_Dev and VideoCapture_Dev.

ppapi/cpp/dev/audio_input_dev.h

Index: ppapi/cpp/dev/audio_input_dev.h
diff --git a/ppapi/cpp/dev/audio_input_dev.h b/ppapi/cpp/dev/audio_input_dev.h
index 2a51eb740e002e3306bdf917eeeda3b127aa89b0..2fc79c6fba6b54fdba2596e05633a9e1bac076ab 100644
--- a/ppapi/cpp/dev/audio_input_dev.h
+++ b/ppapi/cpp/dev/audio_input_dev.h
@@ -23,6 +23,12 @@ class AudioInput_Dev : public Resource {
                  PPB_AudioInput_Callback callback,
                  void* user_data);
 
+  /// Static function for determining whether the browser supports the required
+  /// AudioInput interface.
+  ///
+  /// @return true if the interface is available, false otherwise.
+  static bool IsAvailable();
+
   /// Getter function for returning the internal <code>PPB_AudioConfig</code>
   /// struct.
   ///