[Chromecast] Add volume step interval getter to AvSettings.

chromecast/public/avsettings.h

Index: chromecast/public/avsettings.h
diff --git a/chromecast/public/avsettings.h b/chromecast/public/avsettings.h
index d0e71b732c9cb66596571a5e517fb0bd5505edb9..443496eb0368d700546b382882c3f80ada5d9524 100644
--- a/chromecast/public/avsettings.h
+++ b/chromecast/public/avsettings.h
@@ -103,9 +103,14 @@ class AvSettings {
     // disconnected to HDMI sinks
     AUDIO_VOLUME_CONTROL_TYPE_CHANGED = 5,
 
+    // This event shall be fired whenever the volume step interval provided
+    // by the device is changed, for e.g. when connecting to an AVR setup
+    // where step interval should be 1%.
+    AUDIO_VOLUME_STEP_INTERVAL_CHANGED = 6,

[gfhuang, 2016/01/20 22:48:22]

I think you should just give up ordering and use next one, i.e. 7

it's general good practice not to change existing enums

+
     // This event shall be fired whenever wake-on-cast status is changed by
     // platform.
-    WAKE_ON_CAST_CHANGED = 6,
+    WAKE_ON_CAST_CHANGED = 7,
 
     // This event should be fired when the device is connected to HDMI sinks.
     HDMI_CONNECTED = 100,
@@ -177,6 +182,18 @@ class AvSettings {
   // Nexus Player which is fixed volume.
   virtual AudioVolumeControlType GetAudioVolumeControlType() = 0;
 
+  // Retrieves the volume step interval as percentage in range [0.0, 1.0] that
+  // specifies how much volume to change per step. Returns true if a valid
+  // interval is specified by platform; returns false if interval should defer
+  // to default values.
+  //
+  // Current default volume step intervals per control type are as follows:
+  //  - MASTER_VOLUME (5%)

[gfhuang, 2016/01/20 22:48:22]

"5%" -> "5%, i.e. 0.05" to make it more clear in the range of [0.0, 1.0]

+  //  - ATTENUATION_VOLUME (2%)
+  //  - FIXED_VOLUME (1%)
+  //  - UNKNOWN_VOLUME (1%)
+  virtual bool GetAudioVolumeStepInterval(float* step_inteval) = 0;
+
   // Returns the current volume level, which must be from 0.0 (inclusive) to
   // 1.0 (inclusive).
   virtual float GetAudioVolume() = 0;