Printing: Fix undefined behavior for near 0 scaling

components/printing/renderer/print_web_view_helper.cc

Index: components/printing/renderer/print_web_view_helper.cc
diff --git a/components/printing/renderer/print_web_view_helper.cc b/components/printing/renderer/print_web_view_helper.cc
index 3e77142273bf41af06906e9d9f0b6a56ea6718b5..582cf5bf25b6adb18ba6a1eae7c3f20a2dc2000c 100644
--- a/components/printing/renderer/print_web_view_helper.cc
+++ b/components/printing/renderer/print_web_view_helper.cc
@@ -114,6 +114,8 @@ int GetDPI(const PrintMsg_Print_Params* print_params) {
 #endif  // defined(OS_MACOSX)
 }
 
+constexpr double kEpsilon = 0.01f;

[Lei Zhang, 2016/10/29 01:19:24]

Sorry, I meant line 115 in the header file, that way you can still use the
constant in print_web_view_helper_mac.mm.

CalculatePageLayoutFromPrintParams() will have to change to refer to it as
PrintWebViewHelper::kEpsilon.

[rbpotter, 2016/10/31 16:30:24]

Done.

+
 bool PrintMsg_Print_Params_IsValid(const PrintMsg_Print_Params& params) {
   return !params.content_size.IsEmpty() && !params.page_size.IsEmpty() &&
          !params.printable_area.IsEmpty() && params.document_cookie &&
@@ -234,7 +236,7 @@ void CalculatePageLayoutFromPrintParams(
   int content_height = params.content_size.height();
   // Scale the content to its normal size for purpose of computing page layout.
   // Otherwise we will get negative margins.
-  if (scale_factor > 0 && (fit_to_page || params.print_to_pdf)) {
+  if (scale_factor >= kEpsilon && (fit_to_page || params.print_to_pdf)) {
     content_width =
         static_cast<int>(static_cast<double>(content_width) * scale_factor);
     content_height =
@@ -721,7 +723,7 @@ PrepareFrameAndViewForPrint::PrepareFrameAndViewForPrint(
     frame->printBegin(web_print_params_, node_to_print_);
     double scale_factor = 1.0f;
 #if defined(ENABLE_PRINT_PREVIEW)
-    if (print_params.scale_factor > 0)
+    if (print_params.scale_factor >= kEpsilon)
       scale_factor = print_params.scale_factor;
 #endif
     print_params = CalculatePrintParamsForCss(
@@ -1232,7 +1234,7 @@ bool PrintWebViewHelper::CreatePreviewDocument() {
 
   PageSizeMargins default_page_layout;
   double scale_factor =
-      print_params.scale_factor > 0 ? print_params.scale_factor : 1.0f;
+      print_params.scale_factor >= kEpsilon ? print_params.scale_factor : 1.0f;
 
   ComputePageLayoutInPointsForCss(print_preview_context_.prepared_frame(), 0,
                                   print_params, ignore_css_margins_,
@@ -1828,7 +1830,7 @@ void PrintWebViewHelper::PrintPageInternal(
 
   double css_scale_factor = 1.0f;
 #if defined(ENABLE_PRINT_PREVIEW)
-    if (params.params.scale_factor > 0)
+    if (params.params.scale_factor >= kEpsilon)
       css_scale_factor = params.params.scale_factor;
 #endif
   ComputePageLayoutInPointsForCss(frame, params.page_number, params.params,