Fixing/disabling Windows x64 warnings

Disabled MSVC #4267 warnings in common.gypi to enable x64 builds
for Windows.
Fixed MSVC #4267 warnings in test/testsupport.
Added third_party/directxsdk to .gitignore.

With http://review.webrtc.org/1070008 landed, this should make it possible
to build for x64 on Windows.

BUG=1348
TEST=Compiling with http://review.webrtc.org/1070008 applied:
set GYP_DEFINES="target_arch=x64"
set GYP_GENERATORS=ninja
gclient sync
ninja -C out\Debug_x64

Review URL: https://webrtc-codereview.appspot.com/1060008

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3464 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/test/testsupport/frame_reader.cc b/test/testsupport/frame_reader.cc
index b05ea58..8fea9f3 100644
--- a/test/testsupport/frame_reader.cc
+++ b/test/testsupport/frame_reader.cc
@@ -30,7 +30,7 @@
 
 bool FrameReaderImpl::Init() {
   if (frame_length_in_bytes_ <= 0) {
-    fprintf(stderr, "Frame length must be >0, was %d\n",
+    fprintf(stderr, "Frame length must be >0, was %zu\n",
             frame_length_in_bytes_);
     return false;
   }
@@ -46,7 +46,8 @@
     fprintf(stderr, "Found empty file: %s\n", input_filename_.c_str());
     return false;
   }
-  number_of_frames_ = source_file_size / frame_length_in_bytes_;
+  number_of_frames_ = static_cast<int>(source_file_size /
+                                       frame_length_in_bytes_);
   return true;
 }