Remove trailing whitespace.

Also adds a presubmit to prevent adding trailing whitespace to source
code in the future.

Change-Id: I41a4df81487f6f00aa19b188f0cac6a3377efde6
Reviewed-on: https://skia-review.googlesource.com/57380
Reviewed-by: Ravi Mistry <rmistry@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
diff --git a/src/gpu/mtl/GrMtlCaps.h b/src/gpu/mtl/GrMtlCaps.h
index b793159..75bb2e7 100644
--- a/src/gpu/mtl/GrMtlCaps.h
+++ b/src/gpu/mtl/GrMtlCaps.h
@@ -60,7 +60,7 @@
 
 private:
     void initFeatureSet(MTLFeatureSet featureSet);
- 
+
     void initGrCaps(const id<MTLDevice> device);
     void initShaderCaps();
     void initSampleCount();