Re-enable several MSVC warnings

core/fpdfapi/fpdf_page/fpdf_page.cpp

Index: core/fpdfapi/fpdf_page/fpdf_page.cpp
diff --git a/core/fpdfapi/fpdf_page/fpdf_page.cpp b/core/fpdfapi/fpdf_page/fpdf_page.cpp
index 2cec0928ddae5680fe2c1d9b1b04c9a09078caf6..4f9151f1e90defec0ecb1318cf6b4a8cb5691c79 100644
--- a/core/fpdfapi/fpdf_page/fpdf_page.cpp
+++ b/core/fpdfapi/fpdf_page/fpdf_page.cpp
@@ -713,7 +713,12 @@ void CPDF_Page::GetDisplayMatrix(CFX_Matrix& matrix,
     return;
   }
   CFX_Matrix display_matrix;
-  int x0, y0, x1, y1, x2, y2;
+  int x0 = 0;

[Tom Sepez, 2016/03/16 18:34:58]

I suspect this is only required because iRotate is signed and the compiler
worries that iRotate % 4 could be less than 0, and not covered in the switch. 
If we made this an unsigned type, can we avoid the initialiations here? how far
up does that ripple?

If we don't have to intialize here, we'd catch the case when someone
accidentally deletes one of the assignments in the switch.

[Wei Li, 2016/03/17 02:24:04]

I wish the compiler could be smarter. Unfortunately, it doesn't seem doing more
static analysis in this case. Changing to unsigned, or even enum won't help. 

+  int y0 = 0;
+  int x1 = 0;
+  int y1 = 0;
+  int x2 = 0;
+  int y2 = 0;
   iRotate %= 4;
   switch (iRotate) {
     case 0: