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.cpp b/services/surfaceflinger/GLExtensions.cpp
index 850866a..493122d 100644
--- a/services/surfaceflinger/GLExtensions.cpp
+++ b/services/surfaceflinger/GLExtensions.cpp
@@ -92,6 +92,10 @@
         // hack for Adreno 200
         mHaveTextureExternal = true;
     }
+
+    if (hasExtension("GL_OES_framebuffer_object")) {
+        mHaveFramebufferObject = true;
+    }
 }
 
 bool GLExtensions::hasExtension(char const* extension) const