Remove redundant SupportsWeakPtr from BrowserControlsOffsetManager

BrowserControlsOffsetManager unnecessarily inherits from SupportsWeakPtr.

BUG=None
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2833383002
Cr-Commit-Position: refs/heads/master@{#466698}

cc/input/browser_controls_offset_manager.h

@@ -8,7 +8,6 @@
 #include <memory>
 
 #include "base/macros.h"
-#include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "cc/input/browser_controls_state.h"
 #include "cc/layers/layer_impl.h"
@@ -20,8 +19,7 @@ namespace cc {
 class BrowserControlsOffsetManagerClient;
 
 // Manages the position of the browser controls.
-class CC_EXPORT BrowserControlsOffsetManager
-    : public base::SupportsWeakPtr<BrowserControlsOffsetManager> {
+class CC_EXPORT BrowserControlsOffsetManager {
  public:
   enum AnimationDirection { NO_ANIMATION, SHOWING_CONTROLS, HIDING_CONTROLS };