Refactor OS_LINUX preprocessor directive for LaCrOS effort.

Currently, ChromeOS defines the OS_LINUX directive as well as
OS_CHROMEOS.  We're working to separate these two, so we're
making the fact that OS_LINUX == OS_LINUX || OS_CHROMEOS
explicit.

This is changes for /gpu/ipc/common/gpu_memory_buffer_support.h

This CL was uploaded by git cl split.

R=dcastagna@chromium.org

Bug: 1110266
Change-Id: I5b10a6b731b816cbeacbb7a11916c93f33f40ae5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2370728Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Sean McAllister <smcallis@google.com>
Cr-Commit-Position: refs/heads/master@{#801632}

gpu/ipc/common/gpu_memory_buffer_support.h

@@ -16,7 +16,7 @@
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/gpu_memory_buffer.h"
 
-#if defined(OS_LINUX) || defined(USE_OZONE)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(USE_OZONE)
 namespace gfx {
 class ClientNativePixmapFactory;
 }
@@ -38,7 +38,7 @@ class GPU_EXPORT GpuMemoryBufferSupport {
   bool IsNativeGpuMemoryBufferConfigurationSupported(gfx::BufferFormat format,
                                                      gfx::BufferUsage usage);
 
-#if defined(OS_LINUX) || defined(USE_OZONE)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(USE_OZONE)
   gfx::ClientNativePixmapFactory* client_native_pixmap_factory() {
     return client_native_pixmap_factory_.get();
   }
@@ -62,7 +62,7 @@ class GPU_EXPORT GpuMemoryBufferSupport {
       GpuMemoryBufferImpl::DestructionCallback callback);
 
  private:
-#if defined(OS_LINUX) || defined(USE_OZONE)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(USE_OZONE)
   std::unique_ptr<gfx::ClientNativePixmapFactory> client_native_pixmap_factory_;
 #endif