Add clear function to TestAtlasTextRendering interface

Bug: skia:
Change-Id: I24563abe5e72e57e6764ddf6aca76ccf098cc488
Reviewed-on: https://skia-review.googlesource.com/73640
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/tools/gpu/atlastext/TestAtlasTextRenderer.h b/tools/gpu/atlastext/TestAtlasTextRenderer.h
index 068a60d..6ba4326 100644
--- a/tools/gpu/atlastext/TestAtlasTextRenderer.h
+++ b/tools/gpu/atlastext/TestAtlasTextRenderer.h
@@ -27,6 +27,9 @@
 
     /** Makes a SkBitmap of the target handle's contents. */
     virtual SkBitmap readTargetHandle(void* targetHandle) = 0;
+
+    /** Clears the target to the specified color, encoded as RGBA (low to high byte order) */
+    virtual void clearTarget(void* targetHandle, uint32_t color) = 0;
 };
 
 }  // namespace sk_gpu_test