Add GLES2Implemention::FreeUnusedSharedMemory

gpu/command_buffer/client/fenced_allocator.h

Index: gpu/command_buffer/client/fenced_allocator.h
diff --git a/gpu/command_buffer/client/fenced_allocator.h b/gpu/command_buffer/client/fenced_allocator.h
index 70d85f64a8b0d87e1ab9d35bfc50f3843dc32d64..0115bfa44bdbe21815ed30732ec4ad13edd68fa2 100644
--- a/gpu/command_buffer/client/fenced_allocator.h
+++ b/gpu/command_buffer/client/fenced_allocator.h
@@ -78,6 +78,9 @@ class FencedAllocator {
   // testing.
   bool CheckConsistency();
 
+  // True if any memory is allocated.
+  bool InUse();
+
  private:
   // Status of a block of memory, for book-keeping.
   enum State {
@@ -231,6 +234,11 @@ class FencedAllocatorWrapper {
     return allocator_.CheckConsistency();
   }
 
+  // True if any memory is allocated.
+  bool InUse() {
+    return allocator_.InUse();
+  }
+
   FencedAllocator &allocator() { return allocator_; }
 
  private: