Implement GL_EXT_debug_marker for RendererGL.

Passes dEQP-GLES2.functional.debug_marker.*

Change-Id: I37f2b6724f32867d2e428613b1b6d9c8377c6d60
Reviewed-on: https://chromium-review.googlesource.com/302990
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/renderer/gl/RendererGL.cpp b/src/libANGLE/renderer/gl/RendererGL.cpp
index f6a67d5..6a8ab11 100644
--- a/src/libANGLE/renderer/gl/RendererGL.cpp
+++ b/src/libANGLE/renderer/gl/RendererGL.cpp
@@ -303,19 +303,20 @@
     return new SamplerGL(mFunctions, mStateManager);
 }
 
-void RendererGL::insertEventMarker(GLsizei, const char *)
+void RendererGL::insertEventMarker(GLsizei length, const char *marker)
 {
-    UNREACHABLE();
+    mFunctions->debugMessageInsert(GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_MARKER, 0,
+                                   GL_DEBUG_SEVERITY_NOTIFICATION, length, marker);
 }
 
-void RendererGL::pushGroupMarker(GLsizei, const char *)
+void RendererGL::pushGroupMarker(GLsizei length, const char *marker)
 {
-    UNREACHABLE();
+    mFunctions->pushDebugGroup(GL_DEBUG_SOURCE_APPLICATION, 0, length, marker);
 }
 
 void RendererGL::popGroupMarker()
 {
-    UNREACHABLE();
+    mFunctions->popDebugGroup();
 }
 
 void RendererGL::notifyDeviceLost()