camera2: Add camera client eviction enforcement.

- This updates the CameraService to implement client
  eviction behavior based on process priority.

Bug: 19186859

Change-Id: I646939b1cdf1a2237c4e5044164d55a2542cf36e
diff --git a/include/camera/CameraParameters.h b/include/camera/CameraParameters.h
index c6074fc..ba33ffe 100644
--- a/include/camera/CameraParameters.h
+++ b/include/camera/CameraParameters.h
@@ -108,6 +108,9 @@
      */
     void getSupportedPreviewFormats(Vector<int>& formats) const;
 
+    // Returns true if no keys are present
+    bool isEmpty() const;
+
     // Parameter keys to communicate between camera application and driver.
     // The access (read/write, read only, or write only) is viewed from the
     // perspective of applications, not driver.