Enable anti-alias in WebGL if only GL_EXT_multisampled_render_to_texture is supported.

Source/platform/graphics/gpu/DrawingBuffer.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 76 matching lines @@
 } // namespace
 
 PassRefPtr<DrawingBuffer> DrawingBuffer::create(PassOwnPtr<WebGraphicsContext3D> context, const IntSize& size, PreserveDrawingBuffer preserve, WebGraphicsContext3D::Attributes requestedAttributes, PassRefPtr<ContextEvictionManager> contextEvictionManager)
 {
     ASSERT(context);
     OwnPtr<Extensions3DUtil> extensionsUtil = Extensions3DUtil::create(context.get());
     if (!extensionsUtil) {
         // This might be the first time we notice that the WebGraphicsContext3D is lost.
         return nullptr;
     }
-    bool multisampleSupported = extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample")
+    bool multisampleSupported = (extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample")
+        || extensionsUtil->supportsExtension("GL_EXT_multisampled_render_to_texture"))
         && extensionsUtil->supportsExtension("GL_OES_rgb8_rgba8");
     if (multisampleSupported) {
-        extensionsUtil->ensureExtensionEnabled("GL_CHROMIUM_framebuffer_multisample");
         extensionsUtil->ensureExtensionEnabled("GL_OES_rgb8_rgba8");
+        if (extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample")
+            extensionsUtil->ensureExtensionEnabled("GL_CHROMIUM_framebuffer_multisample");
+        else
+            extensionsUtil->ensureExtensionEnabled("GL_EXT_multisampled_render_to_texture");

[Ken Russell (switch to Gerrit), 2014/11/05 01:36:10]

This isn't syntactially correct. Please don't upload code until you've tested it
locally.

     }
     bool packedDepthStencilSupported = extensionsUtil->supportsExtension("GL_OES_packed_depth_stencil");
     if (packedDepthStencilSupported)
         extensionsUtil->ensureExtensionEnabled("GL_OES_packed_depth_stencil");
     bool discardFramebufferSupported = extensionsUtil->supportsExtension("GL_EXT_discard_framebuffer");
     if (discardFramebufferSupported)
         extensionsUtil->ensureExtensionEnabled("GL_EXT_discard_framebuffer");
 
     RefPtr<DrawingBuffer> drawingBuffer = adoptRef(new DrawingBuffer(context, extensionsUtil.release(), multisampleSupported, packedDepthStencilSupported, discardFramebufferSupported, preserve, requestedAttributes, contextEvictionManager));
     if (!drawingBuffer->initialize(size)) {
@@ skipping 948 matching lines @@
 void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
 {
     if (info->imageId) {
         m_context->releaseTexImage2DCHROMIUM(GL_TEXTURE_2D, info->imageId);
         m_context->destroyImageCHROMIUM(info->imageId);
         info->imageId = 0;
     }
 }
 
 } // namespace blink