Moving GraphicsContext and dependencies from core to platform.

Source/platform/graphics/DiscardablePixelRef.h

Index: Source/platform/graphics/DiscardablePixelRef.h
diff --git a/Source/core/platform/graphics/DiscardablePixelRef.h b/Source/platform/graphics/DiscardablePixelRef.h
similarity index 93%
rename from Source/core/platform/graphics/DiscardablePixelRef.h
rename to Source/platform/graphics/DiscardablePixelRef.h
index 0c6a639ae032d01545aa7cd30d85cc96fee75935..d1dd847b12c6a3464dc60158ff4fe98bd44fd8b6 100644
--- a/Source/core/platform/graphics/DiscardablePixelRef.h
+++ b/Source/platform/graphics/DiscardablePixelRef.h
@@ -29,6 +29,7 @@
 #include "SkBitmap.h"
 #include "SkPixelRef.h"
 
+#include "platform/PlatformExport.h"
 #include "public/platform/WebDiscardableMemory.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
@@ -36,7 +37,7 @@
 namespace WebCore {
 
 // Class for allocating the DiscardablePixelRef object.
-class DiscardablePixelRefAllocator : public SkBitmap::Allocator {
+class PLATFORM_EXPORT DiscardablePixelRefAllocator : public SkBitmap::Allocator {
     // SkBitmap::Allocator implementation. The discardable memory allocated
     // after this call is locked and will not be purged until next
     // onUnlockPixels().
@@ -44,7 +45,7 @@ class DiscardablePixelRefAllocator : public SkBitmap::Allocator {
 };
 
 // PixelRef object whose memory can be discarded when pixels are unlocked.
-class DiscardablePixelRef : public SkPixelRef {
+class PLATFORM_EXPORT DiscardablePixelRef : public SkPixelRef {
 public:
     DiscardablePixelRef(PassOwnPtr<SkMutex>);
     ~DiscardablePixelRef();