refactored screenshot code

the core screenshot function now can capture the screen at any lower resolution
performing bilinear filtering.

we also now have some client code to interface with the screenshot service.

it's now possible to request a screenshot at a lower resolution.

Change-Id: I5a3b0e431421800e3aad601d9af8f94adffbc71f
diff --git a/services/surfaceflinger/LayerBase.cpp b/services/surfaceflinger/LayerBase.cpp
index 3d049a7..14191cb 100644
--- a/services/surfaceflinger/LayerBase.cpp
+++ b/services/surfaceflinger/LayerBase.cpp
@@ -326,6 +326,12 @@
     onDraw(clip);
 }
 
+void LayerBase::drawForSreenShot() const
+{
+    const DisplayHardware& hw(graphicPlane(0).displayHardware());
+    onDraw( Region(hw.bounds()) );
+}
+
 void LayerBase::clearWithOpenGL(const Region& clip, GLclampf red,
                                 GLclampf green, GLclampf blue,
                                 GLclampf alpha) const