scanning: Fix page size dimensions

Update the Letter page size dimensions to be more precise instead of
rounding to the nearest integer. Also, add in some margin when
determining whether a scan area can support a page size in case there
are slight differences due to rounding.

Bug: 171813619
Change-Id: Ie82e8cd28c94540b909884f6f7e89789769bbe22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2504549
Auto-Submit: Jesse Schettler <jschettler@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Jesse Schettler <jschettler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821865}

chrome/browser/chromeos/scanning/scanning_type_converters.cc

@@ -13,10 +13,14 @@ namespace {
 
 namespace mojo_ipc = chromeos::scanning::mojom;
 
+// The margin allowed when comparing a scannable area dimension to a page size
+// dimension. Accounts for differences due to rounding.
+constexpr double kMargin = 1;
+
 // POD struct for page size dimensions in mm.
 struct PageSize {
-  int width;
-  int height;
+  double width;
+  double height;
 };
 
 // ISO A4: 210 x 297 mm.
@@ -25,16 +29,17 @@ constexpr PageSize kIsoA4PageSize = {
     297,
 };
 
-// NA Letter: 216 x 279 mm.
+// NA Letter: 215.9 x 279.4 mm.
 constexpr PageSize kNaLetterPageSize = {
-    216,
-    279,
+    215.9,
+    279.4,
 };
 
 // Returns true if |area| is large enough to support |page_size|.
 bool AreaSupportsPageSize(const lorgnette::ScannableArea& area,
                           const PageSize& page_size) {
-  return area.width() >= page_size.width && area.height() >= page_size.height;
+  return area.width() + kMargin >= page_size.width &&
+         area.height() + kMargin >= page_size.height;
 }
 
 // Returns the page sizes the given |area| supports.

chrome/browser/chromeos/scanning/scanning_type_converters_unittest.cc

@@ -190,8 +190,8 @@ INSTANTIATE_TEST_SUITE_P(
                                            297},
                     ScanSettingsTestParams{mojo_ipc::ColorMode::kGrayscale,
                                            lorgnette::MODE_GRAYSCALE,
-                                           mojo_ipc::PageSize::kNaLetter, 216,
-                                           279},
+                                           mojo_ipc::PageSize::kNaLetter, 215.9,
+                                           279.4},
                     ScanSettingsTestParams{mojo_ipc::ColorMode::kColor,
                                            lorgnette::MODE_COLOR,
                                            mojo_ipc::PageSize::kMax, 0, 0}));