Added a read pixels test.

tests/angle_tests/ReadPixelsTest.cpp

+#include "ANGLETest.h"
+
+class ReadPixelsTest : public ANGLETest
+{
+protected:
+    ReadPixelsTest()
+    {
+        setWindowWidth(32);
+        setWindowHeight(32);
+        setConfigRedBits(8);
+        setConfigGreenBits(8);
+        setConfigBlueBits(8);
+        setConfigAlphaBits(8);
+    }
+};
+
+TEST_F(ReadPixelsTest, out_of_bounds)
+{
+    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
+    glClear(GL_COLOR_BUFFER_BIT);
+    EXPECT_GL_NO_ERROR();
+
+    GLsizei pixelsWidth = 32;
+    GLsizei pixelsHeight = 32;
+    std::vector<GLubyte> pixels(pixelsWidth * pixelsHeight * 4);
+
+    glReadPixels(-pixelsWidth / 2, -pixelsHeight / 2, pixelsWidth, pixelsHeight, GL_RGBA, GL_UNSIGNED_BYTE, pixels.data());
+    EXPECT_GL_NO_ERROR();
+
+    for (int y = pixelsHeight / 2; y < pixelsHeight; y++)
+    {
+        for (int x = pixelsWidth / 2; x < pixelsWidth; x++)
+        {
+            const GLubyte* pixel = pixels.data() + ((y * pixelsWidth + x) * 4);
+
+            // Expect that all pixels which fell within the framebuffer are red
+            EXPECT_EQ(pixel[0], 255);
+            EXPECT_EQ(pixel[1], 0);
+            EXPECT_EQ(pixel[2], 0);
+            EXPECT_EQ(pixel[3], 255);
+        }
+    }
+}