Add EXPORT specifier in /third_party/blink/renderer/platform/graphics

To speed up build time on windows component build, I will enable newly added /Zc:dllexportInlines- flag. The flag is similar to -fvisibility-inlines-hidden in gcc/clang.

This flag makes inline member function is not exported if it does not have static local variables. But in few classes of chromium, we need to add additional EXPORT specifier to prevent link failure.

This is a part of effort adding EXPORT speicifer to enable the flag.

Master CL is
https://chromium-review.googlesource.com/c/chromium/src/+/1317069

This CL was uploaded by git cl split.

R=schenney@chromium.org

Bug: 901709
Change-Id: I605f83511671f07dbf464fa1fd151954d6068da1
Reviewed-on: https://chromium-review.googlesource.com/c/1322332Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606034}

third_party/blink/renderer/platform/graphics/gpu/xr_webgl_drawing_buffer.h

@@ -69,7 +69,7 @@ class PLATFORM_EXPORT XRWebGLDrawingBuffer
   void BeginDestruction();
 
  private:
-  struct ColorBuffer : public RefCounted<ColorBuffer> {
+  struct PLATFORM_EXPORT ColorBuffer : public RefCounted<ColorBuffer> {
     ColorBuffer(XRWebGLDrawingBuffer*, const IntSize&, GLuint texture_id);
     ~ColorBuffer();