Eliminate variable shadow warning in ThumbTrack

Summary:
Updated to avoid a repeated use of weak reference resulted in a a shadow warning.
Fixed.

Test Plan: Ensure import presubmit executes cleanly as expected.

Reviewers: #material_components_ios_owners, randallli

Reviewed By: #material_components_ios_owners, randallli

Projects: #material_components_ios

Differential Revision: http://codereview.cc/D100

Author: Ian Gordon

components/private/ThumbTrack/src/MDCThumbTrack.m

@@ -621,11 +621,11 @@ - (void)setValueFromThumbPosition:(CGPoint)position isTap:(BOOL)isTap {
       userGenerated:YES
          completion:^{
            __strong typeof(weakSelf) strongSelf = weakSelf;
-           __strong typeof(strongSelf->_delegate) strongDelegate = strongSelf->_delegate;
+           __strong typeof(strongSelf->_delegate) strongBlockDelegate = strongSelf->_delegate;
            [strongSelf sendDiscreteChangeAction];
-           if (strongSelf && [strongDelegate
+           if (strongSelf && [strongBlockDelegate
                                  respondsToSelector:@selector(thumbTrack:didAnimateToValue:)]) {
-             [strongDelegate thumbTrack:strongSelf didAnimateToValue:value];
+             [strongBlockDelegate thumbTrack:strongSelf didAnimateToValue:value];
            }
          }];
 }