Add support for ES3 MSAA.

include/gpu/gl/GrGLInterface.h

Index: include/gpu/gl/GrGLInterface.h
diff --git a/include/gpu/gl/GrGLInterface.h b/include/gpu/gl/GrGLInterface.h
index 67d6840e423e4dab45213040e243057cf450dff6..de1b29143faa58daa9b85127a47ff8e246797f58 100644
--- a/include/gpu/gl/GrGLInterface.h
+++ b/include/gpu/gl/GrGLInterface.h
@@ -229,7 +229,31 @@ public:
     GLPtr<GrGLReadBufferProc> fReadBuffer;
     GLPtr<GrGLReadPixelsProc> fReadPixels;
     GLPtr<GrGLRenderbufferStorageProc> fRenderbufferStorage;
+
+#if !GR_GL_IGNORE_ES3_MSAA
+    //  On OpenGL ES there are multiple incompatible extensions that add support for MSAA
+    //  and ES3 adds MSAA support to the standard. On an ES3 driver we may still use the
+    //  older extensions for performance reasons or due to ES3 driver bugs. We want the function
+    //  that creates the GrGLInterface to provide all available functions and internally
+    //  we will select among them. They all have a method called glRenderbufferStorageMultisample*.
+    //  So we have separate function pointers for GL_IMG/EXT_multisampled_to_texture,
+    //  GL_CHROMIUM/ANGLE_framebuffer_multisample/ES3, and GL_APPLE_framebuffer_multisample
+    //  variations.
+    //
+    //  If a driver supports multiple GL_ARB_framebuffer_multisample-style extensions then we will
+    //  assume the function pointers for the standard (or equivalent GL_ARB) version have
+    //  been preferred over GL_EXT, GL_CHROMIUM, or GL_ANGLE variations that have reduced
+    //  functionality.
+
+    //  GL_EXT_multisampled_render_to_texture (preferred) or GL_IMG_multisampled_render_to_texture
+    GLPtr<GrGLRenderbufferStorageMultisampleProc> fRenderbufferStorageMultisampleES2EXT;
+    //  GL_APPLE_framebuffer_multisample
+    GLPtr<GrGLRenderbufferStorageMultisampleProc> fRenderbufferStorageMultisampleES2APPLE;
+#endif
+    //  This is used to store the pointer for GL_ARB/EXT/ANGLE/CHROMIUM_framebuffer_multisample or
+    //  the standard function in ES3+ or GL 3.0+.
     GLPtr<GrGLRenderbufferStorageMultisampleProc> fRenderbufferStorageMultisample;
+
     GLPtr<GrGLRenderbufferStorageMultisampleCoverageProc> fRenderbufferStorageMultisampleCoverage;
     GLPtr<GrGLResolveMultisampleFramebufferProc> fResolveMultisampleFramebuffer;
     GLPtr<GrGLScissorProc> fScissor;