[fuchsia] Notify GPU process of changes in memory pressure.

Providing memory pressure information to the GPU process to allow it
to manage caches, etc more effectively.

Bug: 1020698
Change-Id: Ie92c5cb59cfff80a851a65867a8320ad2bcf8917
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2024853
Auto-Submit: Wez <wez@chromium.org>
Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736374}

content/browser/gpu/gpu_process_host.cc

@@ -155,8 +155,13 @@ int GetForgiveMinutes(gpu::GpuMode gpu_mode) {
 // Feature controlling whether or not memory pressure signals will be forwarded
 // to the GPU process.
 const base::Feature kForwardMemoryPressureEventsToGpuProcess{
-    "ForwardMemoryPressureEventsToGpuProcess",
-    base::FEATURE_DISABLED_BY_DEFAULT};
+  "ForwardMemoryPressureEventsToGpuProcess",
+#if defined(OS_FUCHSIA)
+      base::FEATURE_ENABLED_BY_DEFAULT
+#else
+      base::FEATURE_DISABLED_BY_DEFAULT
+#endif
+};
 #endif
 
 // This matches base::TerminationStatus.