Avoid crashing if multiple target popup is empty.

If the bitmap wasn't allocated, return false instead.

BUG=411505

Review URL: https://codereview.chromium.org/879143002

Cr-Commit-Position: refs/heads/master@{#314009}

content/renderer/render_view_impl.cc

@@ -3932,7 +3932,7 @@ bool RenderViewImpl::didTapMultipleTargets(
           touch_rect, target_rects, GetSize(),
           gfx::Rect(webview()->mainFrame()->visibleContentRect()).size(),
           device_scale_factor_ * webview()->pageScaleFactor(), &zoom_rect);
-  if (!new_total_scale)
+  if (!new_total_scale || zoom_rect.IsEmpty())
     return false;
 
   bool handled = false;
@@ -3947,6 +3947,7 @@ bool RenderViewImpl::didTapMultipleTargets(
           RenderThreadImpl::current()->shared_bitmap_manager();
       scoped_ptr<cc::SharedBitmap> shared_bitmap =
           manager->AllocateSharedBitmap(canvas_size);
+      CHECK(!!shared_bitmap);
       {
         SkBitmap bitmap;
         SkImageInfo info = SkImageInfo::MakeN32Premul(canvas_size.width(),