add support for [1974164] Be able to take a screen shot on the device

screenshots are taken using ISurfaceComposer::captureScreen() which returns
the size of the screenshot and an IMemoryHeap containing the data.
screenshots have limitations:
- they will always fail if a secure window is up on screen
- require GL_OES_framebuffer_object extension
- in some situation, video planes won't been captured

Change-Id: I741c68a2d2984fb139039301c3349e6780e2cd58
diff --git a/services/surfaceflinger/GLExtensions.h b/services/surfaceflinger/GLExtensions.h
index bbb284e..c86c66a 100644
--- a/services/surfaceflinger/GLExtensions.h
+++ b/services/surfaceflinger/GLExtensions.h
@@ -39,6 +39,7 @@
     bool mHaveTextureExternal   : 1;
     bool mHaveNpot              : 1;
     bool mHaveDirectTexture     : 1;
+    bool mHaveFramebufferObject : 1;
 
     String8 mVendor;
     String8 mRenderer;
@@ -66,6 +67,10 @@
         return mHaveDirectTexture;
     }
 
+    inline bool haveFramebufferObject() const {
+        return mHaveFramebufferObject;
+    }
+
     void initWithGLStrings(
             GLubyte const* vendor,
             GLubyte const* renderer,