Fix iOS build by centralizing --writePath.

CQ_EXTRA_TRYBOTS=tryserver.skia:Build-Mac10.7-Clang-Arm7-Debug-iOS-Trybot

BUG=skia:
R=mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/452633002
diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index 245aa0e..a5353aa 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -33,7 +33,7 @@
 
 static const int kAutoTuneLoops = -1;
 
-static const int kDefaultLoops = 
+static const int kDefaultLoops =
 #ifdef SK_DEBUG
     1;
 #else
@@ -50,8 +50,6 @@
 
 DEFINE_int32(loops, kDefaultLoops, loops_help_txt().c_str());
 
-DEFINE_string2(writePath, w, "", "If set, write benches here as .pngs.");
-
 DEFINE_int32(samples, 10, "Number of samples to measure for each bench.");
 DEFINE_int32(overheadLoops, 100000, "Loops to estimate timer overhead.");
 DEFINE_double(overheadGoal, 0.0001,