Fix the texture ID reuse issue in HWUI.

Issue: When the layer of previous frame is destroyed, it doesn't clear the
texture id in mBoundTextures[mTextureUnit], so in the next frame, if
glGenTexture returns same texture ID of the previous frame,
the new texture is not bound.

CRs-fixed: 671736

Change-Id: Ifc5fd2115fb1863b3c006ab14b0faabeaeb4eab4
diff --git a/libs/hwui/Caches.cpp b/libs/hwui/Caches.cpp
index f8d3589..b0f4c2c 100644
--- a/libs/hwui/Caches.cpp
+++ b/libs/hwui/Caches.cpp
@@ -554,11 +554,8 @@
     // call, any texture operation will be performed on the default
     // texture (name=0)
 
-    for (int i = 0; i < REQUIRED_TEXTURE_UNITS_COUNT; i++) {
-        if (mBoundTextures[i] == texture) {
-            mBoundTextures[i] = 0;
-        }
-    }
+    unbindTexture(texture);
+
     glDeleteTextures(1, &texture);
 }
 
@@ -566,6 +563,14 @@
     memset(mBoundTextures, 0, REQUIRED_TEXTURE_UNITS_COUNT * sizeof(GLuint));
 }
 
+void Caches::unbindTexture(GLuint texture) {
+    for (int i = 0; i < REQUIRED_TEXTURE_UNITS_COUNT; i++) {
+        if (mBoundTextures[i] == texture) {
+            mBoundTextures[i] = 0;
+        }
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // Scissor
 ///////////////////////////////////////////////////////////////////////////////