drm_hwcomposer: Add DrmMode::SameSize

Helper function to check if two modes have the same size by comparing
the vdisplay and hdisplay of the underlying drmModeModeInfo.

Change-Id: Idb1923e6f7ff42d886f9e851e15fdac99af54fb9
Signed-off-by: Drew Davenport <ddavenport@google.com>

drm/DrmMode.cpp

diff --git a/drm/DrmMode.cpp b/drm/DrmMode.cpp
index 7cbea44..d9fdb37 100644
--- a/drm/DrmMode.cpp
+++ b/drm/DrmMode.cpp
@@ -28,6 +28,11 @@
   return memcmp(&m, &mode_, offsetof(drmModeModeInfo, name)) == 0;
 }
 
+bool DrmMode::SameSize(const DrmMode &mode) const {
+  return (mode_.vdisplay == mode.mode_.vdisplay) &&
+         (mode_.hdisplay == mode.mode_.hdisplay);
+}
+
 auto DrmMode::CreateModeBlob(const DrmDevice &drm)
     -> DrmModeUserPropertyBlobUnique {
   struct drm_mode_modeinfo drm_mode = {};

drm/DrmMode.h

diff --git a/drm/DrmMode.h b/drm/DrmMode.h
index 5450daf..7520824 100644
--- a/drm/DrmMode.h
+++ b/drm/DrmMode.h
@@ -35,6 +35,8 @@
 
   bool operator==(const drmModeModeInfo &m) const;
 
+  bool SameSize(const DrmMode &mode) const;
+
   auto &GetRawMode() const {
     return mode_;
   }