Add auto-white balance locking to the Camera API.

Adds a new camera parameter for locking auto-white balance to its
current value. Also adds a function for checking if auto-white balance
lock is supported by the current platform. Lock semantics match that
of the auto-exposure lock.

Hidden for now.

Change-Id: Id59339a4be84d55c1b0b8473d765b6aa765999b2
diff --git a/libs/camera/CameraParameters.cpp b/libs/camera/CameraParameters.cpp
index 4f3da40..c295315 100644
--- a/libs/camera/CameraParameters.cpp
+++ b/libs/camera/CameraParameters.cpp
@@ -70,6 +70,8 @@
 const char CameraParameters::KEY_EXPOSURE_COMPENSATION_STEP[] = "exposure-compensation-step";
 const char CameraParameters::KEY_AUTO_EXPOSURE_LOCK[] = "auto-exposure-lock";
 const char CameraParameters::KEY_AUTO_EXPOSURE_LOCK_SUPPORTED[] = "auto-exposure-lock-supported";
+const char CameraParameters::KEY_AUTO_WHITEBALANCE_LOCK[] = "auto-whitebalance-lock";
+const char CameraParameters::KEY_AUTO_WHITEBALANCE_LOCK_SUPPORTED[] = "auto-whitebalance-lock-supported";
 const char CameraParameters::KEY_MAX_NUM_METERING_AREAS[] = "max-num-metering-areas";
 const char CameraParameters::KEY_METERING_AREAS[] = "metering-areas";
 const char CameraParameters::KEY_ZOOM[] = "zoom";