Revert of Make the Sk GL context class an abstract base class

src/gpu/gl/mesa/SkMesaGLContext.cpp

Index: src/gpu/gl/mesa/SkMesaGLContext.cpp
diff --git a/src/gpu/gl/mesa/SkMesaGLContext.cpp b/src/gpu/gl/mesa/SkMesaGLContext.cpp
index 8c339c7fac4fc50ac837b4155464b92d6a8e7b69..31402c5a3cf79cd3ebcd392ba5a85c1114583867 100644
--- a/src/gpu/gl/mesa/SkMesaGLContext.cpp
+++ b/src/gpu/gl/mesa/SkMesaGLContext.cpp
@@ -10,6 +10,24 @@
 
 #include "gl/SkMesaGLContext.h"
 #include "gl/GrGLDefines.h"
+
+SkMesaGLContext::AutoContextRestore::AutoContextRestore() {
+    fOldContext = (Context)OSMesaGetCurrentContext();
+    if (fOldContext) {
+        OSMesaGetColorBuffer((OSMesaContext)fOldContext,
+                              &fOldWidth, &fOldHeight,
+                              &fOldFormat, &fOldImage);
+    }
+}
+
+SkMesaGLContext::AutoContextRestore::~AutoContextRestore() {
+    if (fOldContext) {
+        OSMesaMakeCurrent((OSMesaContext)fOldContext, fOldImage,
+                          fOldFormat, fOldWidth, fOldHeight);
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
 
 SkMesaGLContext::SkMesaGLContext()
     : fContext(static_cast<Context>(NULL))