Revert to old behavior for swap buffers

New behavior is preserved with 'syncOrSwap' call

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1606883005

Review URL: https://codereview.chromium.org/1606883005

bench/nanobench.cpp

@@ -156,7 +156,7 @@ struct GPUTarget : public Target {
     void endTiming() override {
         if (this->gl) {
             SK_GL(*this->gl, Flush());
-            this->gl->swapBuffers();
+            this->gl->waitOnSyncOrSwap();
         }
     }
     void fence() override {

include/gpu/gl/SkGLContext.h

@@ -52,6 +52,8 @@ public:
      */
     virtual GrGLuint eglImageToExternalTexture(GrEGLImage) const { return 0; }
 
+    void swapBuffers();
+
     /**
      * The only purpose of this function it to provide a means of scheduling
      * work on the GPU (since all of the subclasses create primary buffers for
@@ -65,7 +67,7 @@ public:
      * not perform some sort of synchronization, depending on whether the
      * drawing surface provided by the platform is double buffered.
      */
-    void swapBuffers();
+    void waitOnSyncOrSwap();
 
     /**
      * This notifies the context that we are deliberately testing abandoning

src/gpu/gl/SkGLContext.cpp

@@ -78,9 +78,13 @@ void SkGLContext::makeCurrent() const {
 }
 
 void SkGLContext::swapBuffers() {
+    this->onPlatformSwapBuffers();
+}
+
+void SkGLContext::waitOnSyncOrSwap() {
     if (!fFenceSync) {
         // Fallback on the platform SwapBuffers method for synchronization. This may have no effect.
-        this->onPlatformSwapBuffers();
+        this->swapBuffers();
         return;
     }