Fix dragging of images out of the browser

When porting StartDragging to Mojo in https://crrev.com/c/2320268, the
image contents weren't being set in the drop data. This resulted in a
link being saved on Windows and an error shown on Linux.

(cherry picked from commit 35b04f213302a76240a199e0b18ff48d8259a10c)

Bug: 1039255, 1132953
Change-Id: I2d21e0424c89306d5df8caf940e93999d16f78f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2444996
Reviewed-by: Avi Drissman <[email protected]>
Commit-Queue: Henrique Ferreiro <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#813645}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461228
Reviewed-by: Henrique Ferreiro <[email protected]>
Cr-Commit-Position: refs/branch-heads/4280@{#139}
Cr-Branched-From: ea420fb963f9658c9969b6513c56b8f47efa1a2a-refs/heads/master@{#812852}
diff --git a/content/browser/renderer_host/drop_data_util.cc b/content/browser/renderer_host/drop_data_util.cc
index e56df58..021f0fc 100644
--- a/content/browser/renderer_host/drop_data_util.cc
+++ b/content/browser/renderer_host/drop_data_util.cc
@@ -117,7 +117,8 @@
         DCHECK(result.file_contents.empty());
 
         const blink::mojom::DragItemBinaryPtr& binary_item = item->get_binary();
-        result.file_contents.reserve(binary_item->data.size());
+        std::vector<uint8_t> contents = binary_item->data;
+        result.file_contents.assign(contents.begin(), contents.end());
         result.file_contents_source_url = binary_item->source_url;
         result.file_contents_filename_extension =
             binary_item->filename_extension.value();