Moving GraphicsContext and dependencies from core to platform.

Source/platform/graphics/gpu/DrawingBuffer.h

Index: Source/platform/graphics/gpu/DrawingBuffer.h
diff --git a/Source/core/platform/graphics/gpu/DrawingBuffer.h b/Source/platform/graphics/gpu/DrawingBuffer.h
similarity index 96%
rename from Source/core/platform/graphics/gpu/DrawingBuffer.h
rename to Source/platform/graphics/gpu/DrawingBuffer.h
index 2516e28518007ca3f8a2b98b015ac496e690bfee..f1d7afc47deb530c7dddf3333ffb222091db1746 100644
--- a/Source/core/platform/graphics/gpu/DrawingBuffer.h
+++ b/Source/platform/graphics/gpu/DrawingBuffer.h
@@ -31,8 +31,9 @@
 #ifndef DrawingBuffer_h
 #define DrawingBuffer_h
 
-#include "core/platform/graphics/GraphicsContext3D.h"
+#include "platform/PlatformExport.h"
 #include "platform/geometry/IntSize.h"
+#include "platform/graphics/GraphicsContext3D.h"
 #include "platform/graphics/GraphicsTypes3D.h"
 
 #include "public/platform/WebExternalTextureLayerClient.h"
@@ -53,7 +54,7 @@ class GraphicsContext3D;
 class ImageData;
 
 // Abstract interface to allow basic context eviction management
-class ContextEvictionManager : public RefCounted<ContextEvictionManager> {
+class PLATFORM_EXPORT ContextEvictionManager : public RefCounted<ContextEvictionManager> {
 public:
     virtual ~ContextEvictionManager() {};
 
@@ -63,7 +64,7 @@ public:
 
 // Manages a rendering target (framebuffer + attachment) for a canvas.  Can publish its rendering
 // results to a blink::WebLayer for compositing.
-class DrawingBuffer : public RefCounted<DrawingBuffer>, public blink::WebExternalTextureLayerClient  {
+class PLATFORM_EXPORT DrawingBuffer : public RefCounted<DrawingBuffer>, public blink::WebExternalTextureLayerClient  {
     struct MailboxInfo : public RefCounted<MailboxInfo> {
         blink::WebExternalTextureMailbox mailbox;
         unsigned textureId;