Revert of Prefer to use the OES_depth24 extension for WebGL's depth-only back buffers.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
index c42faa8fa3ed28edd72aca2e2666d749b3e2b9df..87a2789becf24be50f74a058344e569300118688 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
@@ -167,19 +167,12 @@
     void addNewMailboxCallback(PassOwnPtr<Closure> closure) { m_newMailboxCallback = std::move(closure); }
 
 protected: // For unittests
-    struct PLATFORM_EXPORT SupportedExtensions {
-        SupportedExtensions();
-
-        bool multisample;
-        bool packedDepthStencil;
-        bool depth24;
-        bool discardFramebuffer;
-    };
-
     DrawingBuffer(
         PassOwnPtr<WebGraphicsContext3D>,
         PassOwnPtr<Extensions3DUtil>,
-        const SupportedExtensions&,
+        bool multisampleExtensionSupported,
+        bool packedDepthStencilExtensionSupported,
+        bool discardFramebufferSupported,
         PreserveDrawingBuffer,
         WebGraphicsContext3D::Attributes requestedAttributes);
 
@@ -306,7 +299,6 @@
     WebGraphicsContext3D::Attributes m_requestedAttributes;
     bool m_multisampleExtensionSupported;
     bool m_packedDepthStencilExtensionSupported;
-    bool m_depth24ExtensionSupported;
     bool m_discardFramebufferSupported;
     Platform3DObject m_fbo;
     // DrawingBuffer's output is double-buffered. m_colorBuffer is the back buffer.