Implement a minimal EGL -> CGL backend

This succesfully renders HelloTriangle and some samples but fails on a
lot of tests. In particular it doesn't handle resizing the window and
doesn't have depth or stencil buffers.

BUG=angleproject:891

Change-Id: I16356471b470f764acb38e8dd3589e9c0129829d
Reviewed-on: https://chromium-review.googlesource.com/290770
Tested-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/renderer/gl/FramebufferGL.cpp b/src/libANGLE/renderer/gl/FramebufferGL.cpp
index ae2a617..35712dc 100644
--- a/src/libANGLE/renderer/gl/FramebufferGL.cpp
+++ b/src/libANGLE/renderer/gl/FramebufferGL.cpp
@@ -35,6 +35,18 @@
     }
 }
 
+FramebufferGL::FramebufferGL(GLuint id,
+                             const gl::Framebuffer::Data &data,
+                             const FunctionsGL *functions,
+                             StateManagerGL *stateManager)
+    : FramebufferImpl(data),
+      mFunctions(functions),
+      mStateManager(stateManager),
+      mFramebufferID(id),
+      mIsDefault(true)
+{
+}
+
 FramebufferGL::~FramebufferGL()
 {
     mStateManager->deleteFramebuffer(mFramebufferID);