Implement FramebufferGL.

BUG=angleproject:885

Change-Id: Ifb5818f185236c671cd7f20ed352edb887b49675
Reviewed-on: https://chromium-review.googlesource.com/258420
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/Framebuffer.cpp b/src/libANGLE/Framebuffer.cpp
index fb7a2de..2a0dd61 100644
--- a/src/libANGLE/Framebuffer.cpp
+++ b/src/libANGLE/Framebuffer.cpp
@@ -82,9 +82,17 @@
 
 Framebuffer::Framebuffer(const Caps &caps, rx::ImplFactory *factory, GLuint id)
     : mData(caps),
-      mImpl(factory->createFramebuffer(mData)),
+      mImpl(nullptr),
       mId(id)
 {
+    if (mId == 0)
+    {
+        mImpl = factory->createDefaultFramebuffer(mData);
+    }
+    else
+    {
+        mImpl = factory->createFramebuffer(mData);
+    }
     ASSERT(mImpl != nullptr);
 }