Enable drawBuffers() also on ES3

BUG=525930
TEST=conformance2/rendering/draw_buffers.html
R=bajones@chromium.org,kbr@chromium.org

Review URL: https://codereview.chromium.org/1315193013

git-svn-id: svn://svn.chromium.org/blink/trunk@201585 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/modules/webgl/WebGLFramebuffer.cpp

@@ -605,8 +605,8 @@ void WebGLFramebuffer::drawBuffers(const Vector<GLenum>& bufs)
 
 void WebGLFramebuffer::drawBuffersIfNecessary(bool force)
 {
-    if (!context()->extensionEnabled(WebGLDrawBuffersName))
-        return;
+    if (context()->isWebGL2OrHigher()
+        || context()->extensionEnabled(WebGLDrawBuffersName)) {
         bool reset = force;
         // This filtering works around graphics driver bugs on Mac OS X.
         for (size_t i = 0; i < m_drawBuffers.size(); ++i) {
@@ -626,6 +626,7 @@ void WebGLFramebuffer::drawBuffersIfNecessary(bool force)
             context()->webContext()->drawBuffersEXT(
                 m_filteredDrawBuffers.size(), m_filteredDrawBuffers.data());
         }
+    }
 }
 
 GLenum WebGLFramebuffer::getDrawBuffer(GLenum drawBuffer)