Revert of Make the Sk GL context class an abstract base class (patchset #4 id:60001 of https://codereview.chromium.org/630843002/)

Reason for revert:
nanobech failing on Android

Original issue's description:
> Make the Sk GL context class an abstract base class
>
> Make the Sk GL context class, SkGLNativeContext, an abstract base class. Before,
> it depended on ifdefs to implement the platform dependent polymorphism.  Move
> the logic to subclasses of the various platform implementations.
>
> This a step to enable Skia embedders to compile dm and bench_pictures. The
> concrete goal is to support running these test apps with Chromium command buffer.
>
> With this change, Chromium can implement its own version of SkGLNativeContext
> that uses command buffer, and host the implementation in its own repository.
>
> Implements the above by renaming the SkGLContextHelper to SkGLContext and
> removing the unneeded SkGLNativeContext. Also removes
> SkGLNativeContext::AutoRestoreContext functionality, it appeared to be unused:
> no use in Skia code, and no tests.
>
> BUG=skia:2992
>
> Committed: https://skia.googlesource.com/skia/+/a90ed4e83897b45d6331ee4c54e1edd4054de9a8

TBR=kkinnunen@nvidia.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:2992

Review URL: https://codereview.chromium.org/639793002
diff --git a/src/gpu/gl/angle/SkANGLEGLContext.cpp b/src/gpu/gl/angle/SkANGLEGLContext.cpp
index 4914ba5..81fcceb 100644
--- a/src/gpu/gl/angle/SkANGLEGLContext.cpp
+++ b/src/gpu/gl/angle/SkANGLEGLContext.cpp
@@ -8,6 +8,21 @@
 
 #include "gl/SkANGLEGLContext.h"
 
+SkANGLEGLContext::AutoContextRestore::AutoContextRestore() {
+    fOldEGLContext = eglGetCurrentContext();
+    fOldDisplay = eglGetCurrentDisplay();
+    fOldSurface = eglGetCurrentSurface(EGL_DRAW);
+
+}
+
+SkANGLEGLContext::AutoContextRestore::~AutoContextRestore() {
+    if (fOldDisplay) {
+        eglMakeCurrent(fOldDisplay, fOldSurface, fOldSurface, fOldEGLContext);
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
 SkANGLEGLContext::SkANGLEGLContext()
     : fContext(EGL_NO_CONTEXT)
     , fDisplay(EGL_NO_DISPLAY)