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

not everything in the video frame is opaque.

R=reed@google.com, sievers@chromium.org
BUG=380680

Review URL: https://codereview.chromium.org/319133003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275511 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/render_widget_host_view_browsertest.cc

@@ -492,7 +492,7 @@ class CompositingRenderWidgetHostViewBrowserTestTabCapture
                                          video_frame->visible_rect().height(),
                                          kPMColor_SkColorType,
                                          kPremul_SkAlphaType));
-    bitmap.allocPixels();
+    bitmap.eraseColor(SK_ColorTRANSPARENT);
     SkCanvas canvas(bitmap);
 
     video_renderer.Paint(video_frame.get(),