Remove un-needed swapBuffers calls in the tests.

src/tests/gl_tests/GLSLTest.cpp

@@ -497,7 +497,6 @@ TEST_P(GLSLTest, ElseIfRewriting)
     ASSERT_NE(0u, program);
 
     drawQuad(program, "a_position", 0.5f);
-    swapBuffers();
 
     EXPECT_PIXEL_EQ(0, 0, 255, 0, 0, 255);
     EXPECT_PIXEL_EQ(getWindowWidth()-1, 0, 0, 255, 0, 255);

src/tests/gl_tests/InstancingTest.cpp

@@ -160,8 +160,6 @@ class InstancingTest : public ANGLETest
         mDrawArraysInstancedANGLE(GL_TRIANGLES, first, count, instanceCount);
 
         ASSERT_GL_NO_ERROR();
-
-        swapBuffers();
     }
 
     virtual void runDrawElementsTest(std::string vs, bool shouldAttribZeroBeInstanced)
@@ -208,7 +206,6 @@ class InstancingTest : public ANGLETest
         // Do the instanced draw
         mDrawElementsInstancedANGLE(GL_TRIANGLES, mIndices.size(), GL_UNSIGNED_SHORT, mIndices.data(), mInstances.size() / 3);
 
-        swapBuffers();
         ASSERT_GL_NO_ERROR();
 
         checkQuads();

src/tests/gl_tests/TextureTest.cpp

@@ -219,7 +219,6 @@ class TextureTest : public ANGLETest
 
         glBindFramebuffer(GL_FRAMEBUFFER, 0);
         drawQuad(m2DProgram, "position", 0.5f);
-        swapBuffers();
 
         int testImageChannels = std::min(sourceImageChannels, destImageChannels);