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/debugger/SkDebugger.h b/debugger/SkDebugger.h
index 7e58047..50ab181 100644
--- a/debugger/SkDebugger.h
+++ b/debugger/SkDebugger.h
@@ -85,7 +85,7 @@
         return fDebugCanvas->getCurrentClip();
     }
 
-    SkRect pictureCull() const   { 
+    SkRect pictureCull() const   {
         return fPicture ? fPicture->cullRect() : SkRect::MakeEmpty();
     }