Bug 1392485: Add REX.R mov to the disassembler. r=handyman

To mitigate risk for beta uplift, the logic here is limited to what we need for QueryDosDeviceW on Win7x64. A better long-term fix would be to combine this with the more general mov logic in the REX.W section.

MozReview-Commit-ID: BykQSYY61Ua

xpcom/build/nsWindowsDllInterceptor.h

@@ -909,7 +909,25 @@ class WindowsDllDetourPatcher
           MOZ_ASSERT_UNREACHABLE("Unrecognized opcode sequence");
           return;
         }
-      } else if (origBytes[nOrigBytes] == 0x45) {
+      } else if (origBytes[nOrigBytes] == 0x44) {
+        // REX.R
+        COPY_CODES(1);
+
+        // TODO: Combine with the "0x89" case below in the REX.W section
+        if (origBytes[nOrigBytes] == 0x89) {
+          // mov r/m32, r32
+          COPY_CODES(1);
+          int len = CountModRmSib(origBytes + nOrigBytes);
+          if (len < 0) {
+            MOZ_ASSERT_UNREACHABLE("Unrecognized opcode sequence");
+            return;
+          }
+          COPY_CODES(len);
+        } else {
+          MOZ_ASSERT_UNREACHABLE("Unrecognized opcode sequence");
+          return;
+        }
+       } else if (origBytes[nOrigBytes] == 0x45) {
         // REX.R & REX.B
         COPY_CODES(1);