ClosePlatformFile() on non-Windows: Return true on success, false on failure

We already did this on Windows, but elsewhere we were returning false
on success and true on failure, because close() returns 0 on success
and -1 on failure, and we were letting that value implicitly convert
to bool.

Bug: webrtc:8719
Change-Id: I417ff207db8d1fa4cf73a49f1d53762a8066da6c
Reviewed-on: https://webrtc-review.googlesource.com/56660
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22150}

rtc_base/platform_file.cc

@@ -63,7 +63,7 @@ FILE* FdopenPlatformFileForWriting(PlatformFile file) {
 }
 
 bool ClosePlatformFile(PlatformFile file) {
-  return close(file);
+  return close(file) == 0;
 }
 
 bool RemoveFile(const std::string& path) {

rtc_base/platform_file.h

@@ -35,7 +35,7 @@ extern const PlatformFile kInvalidPlatformFileValue;
 // the PlatformFile should no longer be used.
 FILE* FdopenPlatformFileForWriting(PlatformFile file);
 
-// Closes a PlatformFile.
+// Closes a PlatformFile. Returns true on success, false on failure.
 // Don't use ClosePlatformFile to close a file opened with FdopenPlatformFile.
 // Use fclose instead.
 bool ClosePlatformFile(PlatformFile file);