Initialize the bitmap before drawing the VideoFrame into it, in case

content/browser/renderer_host/render_widget_host_view_browsertest.cc

Index: content/browser/renderer_host/render_widget_host_view_browsertest.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_browsertest.cc b/content/browser/renderer_host/render_widget_host_view_browsertest.cc
index e054f219cd34f215af4fe1761b5118a5886f3cb5..3f11cb253a136c3067f9a70f62e022b5582a7a89 100644
--- a/content/browser/renderer_host/render_widget_host_view_browsertest.cc
+++ b/content/browser/renderer_host/render_widget_host_view_browsertest.cc
@@ -493,6 +493,7 @@ class CompositingRenderWidgetHostViewBrowserTestTabCapture
                                          kPMColor_SkColorType,
                                          kPremul_SkAlphaType));
     bitmap.allocPixels();

[reed1, 2014/06/06 15:46:30]

While we're editing this file... I see there are two calls to allocPixels! I
think we can eliminate the 2nd one.

[danakj, 2014/06/06 15:47:21]

Well that's strange, haha.

[danakj, 2014/06/06 17:21:08]

Done.

+    bitmap.eraseColor(SK_ColorTRANSPARENT);
     SkCanvas canvas(bitmap);
 
     video_renderer.Paint(video_frame.get(),