Added a DCHECK to validate the metafile page count while handling alp…

…ha blend transparency.

Added a member variable |page_count_| in emf_win.h to track the pages count.

BUG=none
TEST=windows printing works after code changes.

Review URL: http://codereview.chromium.org/6790002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@80167 0039d316-1c4b-4281-b951-d872f2087c98

chrome/renderer/print_web_view_helper_win.cc

@@ -233,6 +233,10 @@ void PrintWebViewHelper::RenderPage(
   skia::VectorPlatformDevice* platform_device =
       static_cast<skia::VectorPlatformDevice*>(device);
   if (platform_device->alpha_blend_used() && !params.supports_alpha_blend) {
+    // Currently, we handle alpha blend transparency for a single page.
+    // Therefore, expecting a metafile with page count 1.
+    DCHECK((*metafile)->GetPageCount() == 1);
+
     // Close the device context to retrieve the compiled metafile.
     if (!(*metafile)->FinishDocument())
       NOTREACHED();

printing/emf_win.cc

@@ -49,7 +49,7 @@ bool DIBFormatNativelySupported(HDC dc, uint32 escape, const BYTE* bits,
   return !!supported;
 }
 
-Emf::Emf() : emf_(NULL), hdc_(NULL) {
+Emf::Emf() : emf_(NULL), hdc_(NULL), page_count_(0) {
 }
 
 Emf::~Emf() {
@@ -421,6 +421,7 @@ bool Emf::StartPage(const gfx::Size& /*page_size*/,
   DCHECK(hdc_);
   if (!hdc_)
     return false;
+  page_count_++;
   PageBreakRecord record(PageBreakRecord::START_PAGE);
   return !!GdiComment(hdc_, sizeof(record),
                       reinterpret_cast<const BYTE *>(&record));

printing/emf_win.h

@@ -70,8 +70,7 @@ class Emf : public NativeMetafile {
   virtual gfx::Rect GetPageBounds(unsigned int page_number) const;
 
   virtual unsigned int GetPageCount() const {
-    // TODO(dpapad): count the number of times StartPage() is called
-    return 1;
+    return page_count_;
   }
 
   virtual HDC context() const {
@@ -106,6 +105,8 @@ class Emf : public NativeMetafile {
   // Valid when generating EMF data through a virtual HDC.
   HDC hdc_;
 
+  int page_count_;
+
   DISALLOW_COPY_AND_ASSIGN(Emf);
 };
 

printing/emf_win_unittest.cc

@@ -141,6 +141,7 @@ TEST_F(EmfPrintingTest, PageBreak) {
       EXPECT_TRUE(emf.FinishPage());
       --pages;
     }
+    EXPECT_EQ(3U, emf.GetPageCount());
     EXPECT_TRUE(emf.FinishDocument());
     size = emf.GetDataSize();
     EXPECT_TRUE(emf.GetDataAsVector(&data));