Revert "Re-land "Move sampler validation to the GL layer.""

Build failure on Linux:

In file included from ../../third_party/angle/src/tests/gl_tests/UniformTest.cpp:7:
In file included from ../../third_party/angle/src/tests/test_utils/ANGLETest.h:10:
../../testing/gtest/include/gtest/gtest.h:1392:16: error: comparison of integers of different signs: 'const int' and 'const unsigned int' [-Werror,-Wsign-compare]
  if (expected == actual) {
      ~~~~~~~~ ^  ~~~~~~
../../testing/gtest/include/gtest/gtest.h:1422:12: note: in instantiation of function template specialization 'testing::internal::CmpHelperEQ<int, unsigned int>' requested here
    return CmpHelperEQ(expected_expression, actual_expression, expected,
           ^
../../third_party/angle/src/tests/gl_tests/UniformTest.cpp:487:5: note: in instantiation of function template specialization 'testing::internal::EqHelper<false>::Compare<int, unsigned int>' requested here
    EXPECT_EQ(GL_SAMPLER_2D, type);
    ^

BUG=angleproject:1123

This reverts commit 6cbf4385280c4c1dd97f0882ecb18dbc4c341fd4.

Change-Id: I95279b37d253e3ea78faa53f3773f2dc3d17df95
Reviewed-on: https://chromium-review.googlesource.com/302030
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/renderer/ProgramImpl.h b/src/libANGLE/renderer/ProgramImpl.h
index a47b18e..47fb9be 100644
--- a/src/libANGLE/renderer/ProgramImpl.h
+++ b/src/libANGLE/renderer/ProgramImpl.h
@@ -66,6 +66,10 @@
     virtual void setUniformMatrix3x4fv(GLint location, GLsizei count, GLboolean transpose, const GLfloat *value) = 0;
     virtual void setUniformMatrix4x3fv(GLint location, GLsizei count, GLboolean transpose, const GLfloat *value) = 0;
 
+    // TODO: The following functions are possibly only applicable to D3D backends. The should be carefully evaluated to
+    // determine if they can be removed from this interface.
+    virtual bool validateSamplers(gl::InfoLog *infoLog, const gl::Caps &caps) = 0;
+
     // Gather uniform block active uniform indices, and uniform block offset info.
     virtual void gatherUniformBlockInfo(std::vector<gl::UniformBlock> *uniformBlocks,
                                         std::vector<gl::LinkedUniform> *uniforms) = 0;