Fix for nexus 5 crashing in GL benches

GLBenches do not expect gl state  to change between onPerCanvasPreDraw and *PostDraw, but we do a clear and sometimes we clear as draw.  This causes us to bind vertex objects / programs / etc.

This change creates two new virtual methods which are called right before and immediately after timing.

BUG=skia:

Review URL: https://codereview.chromium.org/1379853003
diff --git a/tools/VisualBench/VisualLightweightBenchModule.cpp b/tools/VisualBench/VisualLightweightBenchModule.cpp
index d5e4e5b..d54c788 100644
--- a/tools/VisualBench/VisualLightweightBenchModule.cpp
+++ b/tools/VisualBench/VisualLightweightBenchModule.cpp
@@ -169,7 +169,7 @@
 
     fOwner->clear(canvas, SK_ColorWHITE, 2);
 
-    fBenchmark->preDraw();
+    fBenchmark->delayedSetup();
     fRecords.push_back();
 
     // Log bench name
@@ -184,6 +184,7 @@
 
 void VisualLightweightBenchModule::perCanvasPreDraw(SkCanvas* canvas, State nextState) {
     fBenchmark->perCanvasPreDraw(canvas);
+    fBenchmark->preDraw(canvas);
     fCurrentFrame = 0;
     this->nextState(nextState);
 }
@@ -293,6 +294,7 @@
 }
 
 void VisualLightweightBenchModule::postDraw(SkCanvas* canvas) {
+    fBenchmark->postDraw(canvas);
     fBenchmark->perCanvasPostDraw(canvas);
     fBenchmark.reset(nullptr);
     fCurrentSample = 0;