[canvaskit] Remove fringe EGL dependency.

This removes about 5 kb of wasm code size (2 kb gzipped),
20 kb of js code size (4kb gzipped).
I think I can remove getproc (which is a somewhat large
function made up of a lot of string data) with some clever
adjustments of macros in a follow-on CL.

Change-Id: If3a4b30681e13abddea8e84d62297e90316ed7cf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/311817
Reviewed-by: Chris Dalton <csmartdalton@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 2a167c7..5928fed 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -702,6 +702,8 @@
     } else if (skia_use_egl) {
       sources += [ "src/gpu/gl/egl/GrGLMakeNativeInterface_egl.cpp" ]
       libs += [ "EGL" ]
+    } else if (skia_use_webgl) {
+      sources += [ "src/gpu/gl/webgl/GrGLMakeNativeInterface_webgl.cpp" ]
     } else if (is_linux && skia_use_x11) {
       sources += [ "src/gpu/gl/glx/GrGLMakeNativeInterface_glx.cpp" ]
       libs += [ "GL" ]