Fix C++11 Narrowing Errors in WVDrmPlugin

(This contains a merge of http://go/wvgerrit/13382 from the Widevine
repository.)

This undoes the previous change to silence harmless C++11 narrowing
warnings and instead changes the code to no longer trigger them. The
fix was to delcare the type of our PSSH prefix constant to be uint8_t*
and then convert it to char* at usage-time rather than defining the
not-technically-char* data as a char* to start.

Change-Id: I68ff8c3ed0859096863b49c61cd60ae8461b5b29

libwvdrmengine/mediadrm/Android.mk

@@ -1,8 +1,6 @@
 LOCAL_PATH := $(call my-dir)
 include $(CLEAR_VARS)
 
-LOCAL_CLANG_CFLAGS += -Wno-error=c++11-narrowing
-
 LOCAL_SRC_FILES := \
   src/WVDrmPlugin.cpp \
   src/WVGenericCryptoInterface.cpp \

libwvdrmengine/mediadrm/src/WVDrmPlugin.cpp

@@ -170,7 +170,7 @@ status_t WVDrmPlugin::getKeyRequest(
       !InitDataResemblesPSSH(initData)) {
     // This data was passed in the old format, pre-unwrapped. We need to wrap
     // the init data in a new PSSH header.
-    static const char psshPrefix[] = {
+    static const uint8_t psshPrefix[] = {
       0, 0, 0, 0,                                     // Total size
       'p', 's', 's', 'h',                             // "PSSH"
       0, 0, 0, 0,                                     // Flags - must be zero
@@ -178,7 +178,8 @@ status_t WVDrmPlugin::getKeyRequest(
       0xA3, 0xC8, 0x27, 0xDC, 0xD5, 0x1D, 0x21, 0xED,
       0, 0, 0, 0                                      // Size of initData
     };
-    processedInitData.assign(psshPrefix, sizeof(psshPrefix) / sizeof(char));
+    processedInitData.assign(reinterpret_cast<const char*>(psshPrefix),
+                             sizeof(psshPrefix) / sizeof(uint8_t));
     processedInitData.append(reinterpret_cast<const char*>(initData.array()),
                              initData.size());
     const size_t kPsshBoxSizeLocation = 0;