Add helper methods for FBO attachment validation.

Subsequent refactoring will eliminate duplicate code.

BUG=angle:571

Change-Id: I086320beb5c432c326d29d047931575e6f2a1d64
Reviewed-on: https://chromium-review.googlesource.com/205603
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
diff --git a/src/libGLESv2/validationES2.cpp b/src/libGLESv2/validationES2.cpp
index 0d07f0f..76d4802 100644
--- a/src/libGLESv2/validationES2.cpp
+++ b/src/libGLESv2/validationES2.cpp
@@ -839,7 +839,7 @@
     return true;
 }
 
-bool ValidateES2FramebufferTextureParameters(gl::Context *context, GLenum target, GLenum attachment,
+bool ValidateES2FramebufferTextureParameters(const gl::Context *context, GLenum target, GLenum attachment,
                                              GLenum textarget, GLuint texture, GLint level)
 {
     META_ASSERT(GL_DRAW_FRAMEBUFFER == GL_DRAW_FRAMEBUFFER_ANGLE && GL_READ_FRAMEBUFFER == GL_READ_FRAMEBUFFER_ANGLE);
@@ -923,7 +923,7 @@
         }
     }
 
-    gl::Framebuffer *framebuffer = NULL;
+    const gl::Framebuffer *framebuffer = NULL;
     GLuint framebufferHandle = 0;
     if (target == GL_READ_FRAMEBUFFER)
     {