Revert "Use use_x11 feature when preprocessing clipboard.mojom."

This reverts commit e4542cf9.

Reason for revert: Broke Chrome OS.

Original change's description:
> Use use_x11 feature when preprocessing clipboard.mojom.
> 
> The |kSelection| enum value is only available for systems running X11.
> 
> Bug: 676224
> Change-Id: Icdd99c86712d6127a6ae81e74d17b189073e11ed
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2163637
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Reviewed-by: Darwin Huang <huangdarwin@chromium.org>
> Commit-Queue: Lei Zhang <thestig@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#762479}

TBR=dcheng@chromium.org,thestig@chromium.org,huangdarwin@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 676224,1088233
Change-Id: I7ddf3dd99e78d0e5128691d3ef310d09ed848ce6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225846Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774291}

third_party/blink/public/mojom/BUILD.gn

@@ -241,10 +241,6 @@ mojom("mojom_platform") {
     enabled_features = [ "renderer_pref_system_font_family_name" ]
   }
 
-  if (use_x11) {
-    enabled_features += [ "use_x11" ]
-  }
-
   shared_cpp_typemaps = [
     {
       types = [

third_party/blink/public/mojom/clipboard/clipboard.mojom

@@ -20,7 +20,8 @@ enum ClipboardBuffer {
   kStandard,
   // Used on platforms like the X Window System that treat selection
   // as a type of clipboard.
-  [EnableIf=use_x11]
+  // TODO(crbug.com/676224): When preprocessing of mojom is available only
+  // define this value for USE_X11.
   kSelection,
 };
 

third_party/blink/renderer/core/clipboard/system_clipboard.cc

@@ -40,18 +40,12 @@ SystemClipboard::SystemClipboard(LocalFrame* frame)
 }
 
 bool SystemClipboard::IsSelectionMode() const {
-#if defined(USE_X11)
   return buffer_ == mojom::ClipboardBuffer::kSelection;
-#else
-  return false;
-#endif
 }
 
 void SystemClipboard::SetSelectionMode(bool selection_mode) {
-#if defined(USE_X11)
   buffer_ = selection_mode ? mojom::ClipboardBuffer::kSelection
                            : mojom::ClipboardBuffer::kStandard;
-#endif
 }
 
 bool SystemClipboard::CanSmartReplace() {
@@ -249,12 +243,17 @@ bool SystemClipboard::IsValidBufferType(mojom::ClipboardBuffer buffer) {
   switch (buffer) {
     case mojom::ClipboardBuffer::kStandard:
       return true;
-#if defined(USE_X11)
     case mojom::ClipboardBuffer::kSelection:
+#if defined(USE_X11)
       return true;
+#else
+      // Chrome OS and non-X11 unix builds do not support
+      // the X selection clipboard.
+      // TODO(http://crbug.com/361753): remove the need for this case.
+      return false;
 #endif
   }
-  return false;
+  return true;
 }
 
 }  // namespace blink

third_party/blink/renderer/core/clipboard/system_clipboard.h

@@ -35,7 +35,7 @@ class CORE_EXPORT SystemClipboard final
   explicit SystemClipboard(LocalFrame* frame);
   uint64_t SequenceNumber();
   bool IsSelectionMode() const;
-  void SetSelectionMode(bool selection_mode);
+  void SetSelectionMode(bool);
   bool CanSmartReplace();
   bool IsHTMLAvailable();
   Vector<String> ReadAvailableTypes();

ui/base/mojom/clipboard_blink_mojom_traits.h

@@ -25,10 +25,12 @@ struct EnumTraits<blink::mojom::ClipboardBuffer, ui::ClipboardBuffer> {
       case blink::mojom::ClipboardBuffer::kStandard:
         *out = ui::ClipboardBuffer::kCopyPaste;
         return true;
-#if defined(USE_X11)
       case blink::mojom::ClipboardBuffer::kSelection:
+#if defined(USE_X11)
         *out = ui::ClipboardBuffer::kSelection;
         return true;
+#else
+        return false;
 #endif
     }
     return false;