fuchsia: Avoid unnecessary references to WindowEventFilter

The link error I'm trying to avoid is this:

[122->5/127 ~1] SOLINK ./libviews.so
FAILED: libviews.so libviews.so.TOC lib.unstripped/libviews.so
python "../../build/toolchain/gcc_solink_wrapper.py" --readelf="readelf" --nm="nm" --strip=../../third_party/eu-strip/bin/eu-strip --sofile="./lib.unstripped/libviews.so" --tocfile="./libviews.so.TOC" --output="./libviews.so" -- ../../third_party/llvm-build/Release+Asserts/bin/clang++ -shared -Wl,--fatal-warnings -fPIC -Wl,-z,noexecstack -Wl,-z,now -Wl,-z,relro -Wl,-z,defs -Wl,--as-needed -fuse-ld=lld -Wl,-z,max-page-size=4096 -Wl,--icf=all -Wl,--color-diagnostics --target=aarch64-fuchsia -Wl,-z,stack-size=0x800000 -Wl,--no-as-needed -lfdio -Wl,--as-needed -Werror -Wl,--gdb-index -nostdlib++ --sysroot=../../third_party/fuchsia-sdk/sdk/arch/arm64/sysroot -L../../third_party/fuchsia-sdk/sdk/arch/arm64/lib -o "./lib.unstripped/libviews.so" -Wl,-soname="libviews.so" @"./libviews.so.rsp"
ld.lld: error: undefined symbol: views::WindowEventFilter::WindowEventFilter(views::DesktopWindowTreeHost*)
>>> referenced by memory:3118 (../../buildtools/third_party/libc++/trunk/include/memory:3118)
>>>               obj/ui/views/views/desktop_window_tree_host_platform.o:(views::DesktopWindowTreeHostPlatform::OnNativeWidgetCreated(views::Widget::InitParams const&))

ld.lld: error: undefined symbol: views::WindowEventFilter::SetWmMoveResizeHandler(ui::WmMoveResizeHandler*)
>>> referenced by desktop_window_tree_host_platform.cc:106 (../../ui/views/widget/desktop_aura/desktop_window_tree_host_platform.cc:106)
>>>               obj/ui/views/views/desktop_window_tree_host_platform.o:(views::DesktopWindowTreeHostPlatform::OnNativeWidgetCreated(views::Widget::InitParams const&))
clang: error: ld.lld command failed with exit code 1 (use -v to see invocation)

I'm not sure what the correct approach is; DesktopWindowTreeHostPlatform
depends on WindowEventFilter which uses LinuxUI.

Since there's no available non-client area on Fuchsia currently, not
doing this seems correct for the time being. Or does Fuchsia really need
its own DesktopWindowTreeHostFuchsia implementation?

Bug: 808287
Change-Id: I2af683415ea00147607eb4236540d8d3e8643603
Reviewed-on: https://chromium-review.googlesource.com/c/1298554
Commit-Queue: Scott Graham <scottmg@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602860}

ui/views/widget/desktop_aura/desktop_window_tree_host_platform.cc

@@ -5,6 +5,7 @@
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_platform.h"
 
 #include "base/time/time.h"
+#include "build/build_config.h"
 #include "ui/aura/client/drag_drop_client.h"
 #include "ui/aura/client/transient_window_client.h"
 #include "ui/base/hit_test.h"
@@ -16,11 +17,14 @@
 #include "ui/platform_window/platform_window_init_properties.h"
 #include "ui/views/corewm/tooltip_aura.h"
 #include "ui/views/widget/desktop_aura/desktop_native_widget_aura.h"
-#include "ui/views/widget/desktop_aura/window_event_filter.h"
 #include "ui/views/widget/widget_aura_utils.h"
 #include "ui/views/window/native_frame_view.h"
 #include "ui/wm/core/window_util.h"
 
+#if defined(OS_LINUX)
+#include "ui/views/widget/desktop_aura/window_event_filter.h"
+#endif
+
 namespace views {
 
 namespace {
@@ -96,6 +100,7 @@ void DesktopWindowTreeHostPlatform::OnNativeWidgetCreated(
     const Widget::InitParams& params) {
   native_widget_delegate_->OnNativeWidgetCreated(true);
 
+#if defined(OS_LINUX)
   // Setup a non_client_window_event_filter, which handles resize/move, double
   // click and other events.
   DCHECK(!non_client_window_event_filter_);
@@ -108,6 +113,7 @@ void DesktopWindowTreeHostPlatform::OnNativeWidgetCreated(
 
   non_client_window_event_filter_ = std::move(window_event_filter);
   window()->AddPreTargetHandler(non_client_window_event_filter_.get());
+#endif
 }
 
 void DesktopWindowTreeHostPlatform::OnWidgetInitDone() {}