[Printing] Write file to file descriptor directly on Android

Android's policy doesn't allow to exchange file ownership. It should be
caught by our test but we don't have up-to-date bots setup in Chromium
yet.

Bug: 1050064
Change-Id: I26c82e538817e68fd49f40c0c7c414c5a76078b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2048271
Commit-Queue: Shimi Zhang <ctzsm@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740491}

printing/metafile.cc

@@ -45,4 +45,17 @@ bool Metafile::SaveTo(base::File* file) const {
   return true;
 }
 
+#if defined(OS_ANDROID)
+bool Metafile::SaveToFileDescriptor(int fd) const {
+  if (fd == base::kInvalidFd)
+    return false;
+
+  std::vector<char> buffer;
+  if (!GetDataAsVector(&buffer))
+    return false;
+
+  return base::WriteFileDescriptor(fd, buffer.data(), buffer.size());
+}
+#endif  // defined(OS_ANDROID)
+
 }  // namespace printing

printing/metafile.h

@@ -20,6 +20,9 @@
 #include <ApplicationServices/ApplicationServices.h>
 #include <CoreFoundation/CoreFoundation.h>
 #include "base/mac/scoped_cftyperef.h"
+#elif defined(OS_ANDROID)
+#include "base/file_descriptor_posix.h"
+#include "base/files/file_util.h"
 #endif
 
 namespace base {
@@ -93,6 +96,14 @@ class PRINTING_EXPORT MetafilePlayer {
   // called after the metafile is closed. Returns true if writing succeeded.
   virtual bool SaveTo(base::File* file) const = 0;
 
+#if defined(OS_ANDROID)
+  // Similar to bool SaveTo(base::File* file) const, but write the data to the
+  // file descriptor directly. This is because Android doesn't allow file
+  // ownership exchange. This function should ONLY be called after the metafile
+  // is closed. Returns true if writing succeeded.
+  virtual bool SaveToFileDescriptor(int fd) const = 0;
+#endif  // defined(OS_ANDROID)
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MetafilePlayer);
 };
@@ -160,6 +171,9 @@ class PRINTING_EXPORT Metafile : public MetafilePlayer {
   // MetfilePlayer
   bool GetDataAsVector(std::vector<char>* buffer) const override;
   bool SaveTo(base::File* file) const override;
+#if defined(OS_ANDROID)
+  bool SaveToFileDescriptor(int fd) const override;
+#endif  // defined(OS_ANDROID)
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Metafile);

printing/printing_context_android.cc

@@ -13,7 +13,6 @@
 #include "base/android/jni_android.h"
 #include "base/android/jni_array.h"
 #include "base/android/jni_string.h"
-#include "base/files/file.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/string_number_conversions.h"
@@ -159,9 +158,7 @@ void PrintingContextAndroid::ShowSystemDialogDone(
 void PrintingContextAndroid::PrintDocument(const MetafilePlayer& metafile) {
   DCHECK(is_file_descriptor_valid());
 
-  base::File file(fd_);
-  metafile.SaveTo(&file);
-  file.TakePlatformFile();
+  metafile.SaveToFileDescriptor(fd_);
 }
 
 PrintingContext::Result PrintingContextAndroid::UseDefaultSettings() {