GLES: Expose OES_mapbuffer in GLES2 on GLES3.

This extension is mandatory for EXT_map_buffer_range support. We can
emulate it using GLES 3.0 core map functionality.

BUG=angleproject:1751

Change-Id: Idba09ce7276603d5556039f4a49aa0b87cae22aa
Reviewed-on: https://chromium-review.googlesource.com/431826
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/src/tests/gl_tests/BufferDataTest.cpp b/src/tests/gl_tests/BufferDataTest.cpp
index 7707a4a..5ba705d 100644
--- a/src/tests/gl_tests/BufferDataTest.cpp
+++ b/src/tests/gl_tests/BufferDataTest.cpp
@@ -7,6 +7,8 @@
 #include "test_utils/ANGLETest.h"
 #include "test_utils/gl_raii.h"
 
+#include "random_utils.h"
+
 #include <stdint.h>
 
 using namespace angle;
@@ -433,6 +435,54 @@
     EXPECT_GL_NO_ERROR();
 }
 
+// Verify OES_mapbuffer is present if EXT_map_buffer_range is.
+TEST_P(BufferDataTest, ExtensionDependency)
+{
+    if (extensionEnabled("GL_EXT_map_buffer_range"))
+    {
+        ASSERT_TRUE(extensionEnabled("GL_OES_mapbuffer"));
+    }
+}
+
+// Test mapping with the OES extension.
+TEST_P(BufferDataTest, MapBufferOES)
+{
+    if (!extensionEnabled("GL_EXT_map_buffer_range"))
+    {
+        // Needed for test validation.
+        return;
+    }
+
+    std::vector<uint8_t> data(1024);
+    FillVectorWithRandomUBytes(&data);
+
+    GLBuffer buffer;
+    glBindBuffer(GL_ARRAY_BUFFER, buffer.get());
+    glBufferData(GL_ARRAY_BUFFER, data.size(), nullptr, GL_STATIC_DRAW);
+
+    // Validate that other map flags don't work.
+    void *badMapPtr = glMapBufferOES(GL_ARRAY_BUFFER, GL_MAP_READ_BIT);
+    EXPECT_EQ(nullptr, badMapPtr);
+    EXPECT_GL_ERROR(GL_INVALID_ENUM);
+
+    // Map and write.
+    void *mapPtr = glMapBufferOES(GL_ARRAY_BUFFER, GL_WRITE_ONLY_OES);
+    ASSERT_NE(nullptr, mapPtr);
+    ASSERT_GL_NO_ERROR();
+    memcpy(mapPtr, data.data(), data.size());
+    glUnmapBufferOES(GL_ARRAY_BUFFER);
+
+    // Validate data with EXT_map_buffer_range
+    void *readMapPtr = glMapBufferRangeEXT(GL_ARRAY_BUFFER, 0, data.size(), GL_MAP_READ_BIT_EXT);
+    ASSERT_NE(nullptr, readMapPtr);
+    ASSERT_GL_NO_ERROR();
+    std::vector<uint8_t> actualData(data.size());
+    memcpy(actualData.data(), readMapPtr, data.size());
+    glUnmapBufferOES(GL_ARRAY_BUFFER);
+
+    EXPECT_EQ(data, actualData);
+}
+
 // Use this to select which configurations (e.g. which renderer, which GLES major version) these tests should be run against.
 ANGLE_INSTANTIATE_TEST(BufferDataTest, ES2_D3D9(), ES2_D3D11(), ES2_OPENGL(), ES2_OPENGLES());
 ANGLE_INSTANTIATE_TEST(BufferDataTestES3, ES3_D3D11(), ES3_OPENGL(), ES3_OPENGLES());