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

Source/platform/graphics/gpu/DrawingBuffer.cpp

Index: Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/Source/platform/graphics/gpu/DrawingBuffer.cpp b/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 182ba0b004577c248eec139de540030241b2b0e2..71a9d3b1a988919ab823b4fc30879fb51ab149b2 100644
--- a/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -94,11 +94,17 @@ PassRefPtr<DrawingBuffer> DrawingBuffer::create(PassOwnPtr<WebGraphicsContext3D>
         // 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"))

[Ken Russell (switch to Gerrit), 2014/10/31 23:23:42]

The code in DrawingBuffer::initialize already checks for the
GL_EXT_multisampled_render_to_texture extension, and I'm quite sure that code
path has been tested. Is your patch for the case where the hardware can't
support GL_CHROMIUM_framebuffer_multisample, but does support
GL_EXT_multisampled_render_to_texture? Do you have an example of such hardware
on which we could verify this fix?

Could you please file a bug about this and reference crbug.com/322706 ?

         && extensionsUtil->supportsExtension("GL_OES_rgb8_rgba8");
     if (multisampleSupported) {

[Ken Russell (switch to Gerrit), 2014/11/03 22:47:52]

Please factor out the call to ensureExtensionEnabled("GL_OES_rgb8_rgba8") so
it's only called once on this code path.

-        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");
+            extensionsUtil->ensureExtensionEnabled("GL_OES_rgb8_rgba8");
+        } else {
+            extensionsUtil->ensureExtensionEnabled("GL_EXT_multisampled_render_to_texture");
+            extensionsUtil->ensureExtensionEnabled("GL_OES_rgb8_rgba8");
+        }
     }
     bool packedDepthStencilSupported = extensionsUtil->supportsExtension("GL_OES_packed_depth_stencil");
     if (packedDepthStencilSupported)