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/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index f1b42e6..fdfd5a4 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -1440,7 +1440,7 @@
     AutoValidateClip avc(this);
 
     bool isAA = kSoft_ClipEdgeStyle == edgeStyle;
-    
+
     FOR_EACH_TOP_DEVICE(device->clipRRect(rrect, op, isAA));
 
     fMCRec->fRasterClip.op(rrect, fMCRec->fMatrix, this->getTopLayerBounds(), (SkRegion::Op)op,
@@ -1477,7 +1477,7 @@
     AutoValidateClip avc(this);
 
     bool isAA = kSoft_ClipEdgeStyle == edgeStyle;
-    
+
     FOR_EACH_TOP_DEVICE(device->clipPath(path, op, isAA));
 
     const SkPath* rasterClipPath = &path;