Add GPU memory tab to the task manager.

content/public/browser/gpu_data_manager_observer.h

Index: content/public/browser/gpu_data_manager_observer.h
diff --git a/content/public/browser/gpu_data_manager_observer.h b/content/public/browser/gpu_data_manager_observer.h
index 67d8d4a1c23379c05c69ee7a9f414d5ad74a0d7d..c5b1b3d16bf8feda5b4e4156cecbd635e1f051cc 100644
--- a/content/public/browser/gpu_data_manager_observer.h
+++ b/content/public/browser/gpu_data_manager_observer.h
@@ -6,6 +6,7 @@
 #define CONTENT_PUBLIC_BROWSER_GPU_DATA_MANAGER_OBSERVER_H_
 
 #include "content/common/content_export.h"
+#include "content/public/common/gpu_memory_stats.h"
 
 namespace content {
 
@@ -16,6 +17,10 @@ class GpuDataManagerObserver {
   // Called for any observers whenever there is a GPU info update.
   virtual void OnGpuInfoUpdate() = 0;
 
+  // Called for any observers whenever there is a GPU video memory update.
+  virtual void OnVideoMemoryUsageStatsUpdate(
+      const GPUVideoMemoryUsageStats& video_memory_usage_stats) = 0;
+
  protected:
   virtual ~GpuDataManagerObserver() {}
 };