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/Layer.h b/services/surfaceflinger/Layer.h
index 188da6a..caa6d17 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -70,6 +70,7 @@
     // LayerBase interface
     virtual void setGeometry(hwc_layer_t* hwcl);
     virtual void setPerFrameData(hwc_layer_t* hwcl);
+    virtual void drawForSreenShot() const;
     virtual void onDraw(const Region& clip) const;
     virtual uint32_t doTransaction(uint32_t transactionFlags);
     virtual void lockPageFlip(bool& recomputeVisibleRegions);